维系蛋白质分子二级结构的化学键是（）
A.离子键
B.肽键
C.二硫键
D.氢键
E.疏水键
参考答案：D
—You see, I’m poor in maths, you are not good at English, and...
— That’s ____ we should help each other.
A．when
B．where
C．how
D．what
当气体的压力升高，温度降低时其体积增大。
