An aluminum piston has lower inertia and higher coefficient of （） compared to that of cast iron.

A . just B . nearly C . merely D . already

A . improve skirt lubrication B . allow for expansion C . transmit forces evenly D . improve the piston seal

A . Differential B . Trunk C . Barrel D . Valve-in-head

A . inspection covers should not be opened until the engine has cooled B . ventilation system should be continued in operation for one hour for cooling C . scavenge pump should be immediately secured to prevent loss of lube oil D . explosion covers should be opened slightly to provide extra ventilatio

A . sliding block B . pintle C . reaction ring D . tilting box or swash plate

A . twice as large as with a cast iron piston B . the same size as with a cast iron piston C . half as large as with a cast iron piston D . the same size as the crown of an aluminum pisto

A . a high exhaust temperature B . a high smoky exhaust C . a high output D . a high compressio

A . less than B . greater than C . equal to D . twice larger tha

A . suction stroke B . compression stroke C . power stroke D . exhaust stroke

A . thermal B . mechanical C . plastic D . elastic

A . The aluminum will provide greater resistance to the spread of fire by conduction B . The aluminum structure is usually attached to a steel coaming by a method that insulates the two metals C . If the superstructure is stressed，an aluminum structure requires additional expansion joints to prevent fracture D . The steel at the area of the aluminum-to-steel connection must be closely checked for galvanic corrosio

A . Corner fittings B . Framework，primarily the corner posts C . Framework and siding acting as a girder D . Aluminum side and end panel

A . lifted B . reassembled C . dismounted D . disassembled

A . reduce the ring groove wear rate B . seal against crankcase vapors C . lessen the wear on aluminum part of the cylinder D . allow for the greater expansion rate of aluminum

A . greater high temperature strength B . better heat conductivity C . greater weight per cubic inch D . increased resistance to wear

A、an immediate crankcase explosion B、oil contamination in the compressed air C、a decrease in compressor capacity D、no immediate loss of the compressed air capacity

A . build up the piston crown by metal spraying B . build up the cylinder head by metal spraying C . insert shims between the crankpin bearing box and the connecting rod foot D . install a thinner head gasket

A . 正确 B . 错误

A . Hard rubber B . Canvas C . Leather D . Sponge rubber

是 否

The importance of environment in determining an individual's intelligence can be demonstrated by the case history of the identical twins, Peter and Mark. Being identical, the twins had identical brains at birth, end their growth processes were the same. When the twins were three months old, their parents died, and they were placed in separate homes. Peter was reared by parents of low intelligence in an isolated community with poor educational opportunities. Mark, on the other hand, was raised in the home of rich parents who had been to college. He was read to as a child, sent to a good school, and given every opportunity to be stimulated intellectually. This environmental difference continued until the twins were in their late teens, when they were given tests to measure their intelligence. Peter's score was 85, well below the level he might have attained if reared under average conditions. Mark' s score was 125, twenty-five points above the average and fully forty points higher than his identical brother. Given equal opportunities, the twins would have tested at roughly the same level. (38) A．Children reared under average conditions possess average intelligence. B．Lack of opportunity prevents the growth of intelligence. C．An individual's intelligence is determined chiefly by his environment. D．Changes of environment produce changes in the brain structure.

The performance of the US labour market in the late 1990s is as much a feature of the puzzlingly benign so-called New Economy. For the past four years the US has enjoyed an average annual growth rate of 4 percent— up from an average of about 3 percent in the previous decade. Productivity improvements account for about two-thirds of that elevated output, as workers have increased their output per hour. The rest has come from a rapid increase in the total number of workers, what economists call labour inputs. There has been a surge in new jobs—7m in the last three years—that has pushed the unemployment rate down into the uncharted territory of barely 4 percent. Recent economic history suggests that, whenever unemployment has gone this low, the scramble for workers becomes so difficult that wages are rapidly bid up, and an inflationary spiral follows. But in the US in the past five years, wage growth has been muted. In the last year, total employee compensation in the private sector rose by just 3.3 percent, almost unchanged on the figure three years ago, when the unemployment rate was 5.4 percent. "In some ways it's a bigger puzzle than the productivity puzzle," says Paul Krugman, professor of economics at the Massachusetts Institute of Technology. "How can we have such a low unemployment rate without an explosion of wages？" A number of factors appear to have contributed. In their search for workers to fill positions, companies have reached out to places they have not looked at in the past. As a result, more people are working than ever. The proportion of the population in employment reached a record high this year of more than 64 percent. This expanded labour supply helps explain why companies have kept the lid on pay over the last few years. The availability of new sources of labour—women, retirees, college students among them—means companies may not have to give big pay rises to hire new workers. It also helps explain why the benefits of the New Economy are not always widely felt—more people seem to be working longer hours than ever. But an expanded labour supply can only explain part of what has changed in the US in recent years. After all, unemployment—the proportion of the labour force out of work—has still declined, indicating that companies have drawn new workers not just from the pool of those not previously in the labour force, but also from the unemployed. And yet still wage costs have remained muted. One possible explanation is that companies have become more flexible in how they pay. "At Newfield, we use a much broader variety of means to reward workers, including performance related pay, year-end bonuses, and extended contracts," says Mr. Ostop. Why does Connecticut have the tightest labour market in the U. S. ？