The _____ objective of this study was to investigate whether germ cell-derived proteins leak from STs into IF following toxicant-induced damage to spermatogenesis.

A . meaning B . function C . context D . form

Plastic is the panacea of the ages. Nearly every man-made object (1)_____ (2)_____ of, or at least (3)_____ its very structure, to this wonder compound. Rain slickers, computer terminals, automobile engine parts, coffee cups (and the sugar stirrers too), breast implants, toy soldiers—they are all made up of plastic, or one of its many (4)_____ Since the (5)_____ of civilization, humankind bas been experimenting (6)_____ a multifunctional material—one that had to be equally strong and lightweight—to carry, contain and protect valuables. (7)_____ it could carry, contain and protect humans too, even better. Generations of tinkerers and scientists set off (8)_____ the challenge, striking gold some 170 years ago. By mixing natural rubber with sulphur they created the world's most utilized material ever. In developing a (9)_____, malleable and durable substance, the most important inventions of the industrial age were to follow shortly thereafter. The automobile and airplane industries, to (10)_____ just two, owe their very existence to plastic. And, (11)_____ celluloid plastic strips, the Lumiere Brothers would never have brought moving pictures to the big screen. The development of plastic is a story of human (12)_____, ingenuity and luck. (13)_____ the legend now goes, in 1839, the American inventor Charles Goodyear (the famous tyre company would later use his name) was experimenting with the sulphur treatment of natural rubber when he dropped a piece of sulphur-treated rubber on a stove. The heat seemed to give rubber (14)_____ properties. It was stronger, more (15)_____ to abrasions more elastic, much less (16)_____ to temperature, (17)_____ to gases, and highly resistant to chemicals and electric (18)_____ Eyeing this as a cheaply and easily reproduced construction material, a whirlwind of work (19)_____ and the birth of (20)_____ plastic and plastic-derivatives were born from camphor to celluloid to rayon; cellophane, polyvinyl chloride (or PVC); styrofoam and nylon were soon to follow. A．consists B．comprises C．constitutes D．composes

A.idea B.concept C.theory D.thiriking

A．is ambitious and unrealistic B．politically sensitive C．will bring harm to culture D．well cause pollution in the area

A.learning level B.practical activities C.learning strategies D.habits of thinking

A．it may stir a great deal of debate among the Bush Administration B．every unit of the modern military has depended on the heavy use of some kind of electronic equipment C．the Pentagon's concern was understandable D．they had different arguments

A．all trying to show us something B．of different art skills C．of different art styles D．of different acceptance to the public

A．learn all parts of the business B．see that their guests enjoy themselves C．be able to answer all kinds of questions D．keep their important guests happy

A、learning level B、practical activities C、learning strategies D、habits of thinking

A．A.appealed B．B.attracted C．C.addressed D．D.applied

A．functionmodel,classmodelandstatemodel B． classmodel,interactionmodelandstatemodel C． classmodel,interactionmodelandsequencemodel D． functionmodel,interactionmodelandstatemodel