He doubted ______ it was true. A: A.if B: B.that C: C.as though D: D.as if

．The girl ________ long hair is very beautiful． A: A．to B: B．for C: C．as D: D．with

________ is important for us to learn English well． A: A．It B: B．for C: C．as D: D．with

Don’t talk about such things of__________you are not sure. A: A.which B: B.what C: C.as D: D.those

7. 下列原子中半径最大的是： A: A.Ba B: B.Ca C: C.As D: D.At

Nylon fibers last longer and are stronger than natural fibers _______ silk or cotton. A: A.such as B: B.as regards C: C.as well as D: D.as such

Staying in a hotel for a day costs ________ renting in the country for a week． A: A.more twice than B: B.twice as much as C: C.as much as twice D: D.as much twice as

Many young kids are ___________ becoming obese because they eat too much junk food. A: A.in danger B: B.at risk of C: C.as a result of D: D.in fear

比较C≡C, C=C, C─C, C=C─C=C的键长次序为: C=C─C=C>C─C> C≡C >C=C|C=C─C=C>C─C>C=C>C≡C|C≡C>C=C>C─C>C=C─C=C|C─C>C=C>C=C─C=C>C≡C|C─C>C=C─C=C>C=C>C≡C

下列哪种主链骨架原子排列最能代表两个肽键?() A: Cα—N—Cα—C—Cα—N—Cα—C B: Cα—N—C—C—N—Cα C: C—N—Cα—Cα—C—N D: Cα—C—N—Cα—C—N E: Cα—Cα—C—N—Cα—Cα—C