There are two types of social practices. they are _____________ and _____________.

A . Oil Rig chain and Oil Field Stud Link chain B . Flash-butt welded chain and Di-Lok chain C . Flash-butt welded chain and Oil Rig chain D . Oil Field Stud Link chain and Flash-butt welded chai

A .  Shared Distributed Destinations （SDD） B .  Uniform Distributed Destinations （UDD） C .  Weighted Distributed Destinations （WDD） D .  Bounced Distributed Destinations （BDD）

A . U-Type and posilok shackles B . C-Type and wedge shackles C . D-Type and bow shackles D . wedge and kenter shackle

A .  Blocking cipher andnon-blocking cipher B .  CBC cipher and EBC cipher C .  Block cipher and Stream cipher D .  Blocker cipher and Streamer cipher E .  3DES cipher and AES cipher

A . Diurna B . Semi-diurnal C . Solar D . Mixed

A．13-and 26-frame B．26-and 51-frame C．51-and 102-frame

The first is called the "tank test". A modem airplane must fly very high in the sky. Air must be pumped into the plane so that the passengers can breathe. The metal structure (结构) of the plane has to be very strong for this reason. When the plane is filled with air, the air presses against the skin of the plane inside. The pressure (压力) on a small window is like a huge foot that is trying to get out. If a small part of the plane were to fail, the plane would explode in the sky. To test the structure of the plane, the plane is lowered into a huge tank or container of water. Then it is filled with air. The pressure inside the plane is greater than it ever will be when it is high up in the air. Finally, there is an explosion. This does not cause so much damage inside the water tank as it would anywhere else. Engineers can discover which part of the plane has broken. Then that part is made stronger. The most dangerous test happens when the new plane is going through test flights in the air. The test pilot must find out exactly what happens when the engines(发动机) are all shut off at once. The plane begins to fall like a stone. It is the pilot's job to find out how he can get control of the plane again. These two tests are examples of how planes are made safe before they ever carry passengers. By doing the "tank test", the engineers can find out______. A．the amount of air in the plane B．the strength of the plane structure C．the pressure inside and outside the plane D．the power of the airplane engines

是 否

A．Goods B．Materials C．Materials and products D．Raw materlals and finished products