维系蛋白质二级结构稳定的化学键是()。
A.盐键
B.二硫键
C.肽键
D.疏水作用
E.氢键
参考答案:E
Good pencil erasers are soft enough not ______ paper but hard enough so that they crumble gradually when used.
A.by damaging
B.so that they damage
C.to damage
D.damaging
试述幼小衔接工作应注意的问题。