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【多选题】
关于蛋白质二级结构的论述哪些是正确的A.
一种蛋白质分子只存在一种二级结构形式
B.
是多肽链本身折叠盘
C.
主要存在形式有α-螺旋和β-折叠
D.
维持二级结构的化学键是肽键和氢键
E.
二级结构的存在形式是由氨基酸的组成决定
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举一反三
【单选题】They arrived at a farmhouse, ______. [ ]
A.
in front sat a small boy.
B.
in front of it sat a small boy.
C.
in front of which a small boy sat.
D.
sitting in front of which was a small boy.
【单选题】In front of the farmhouse ______. A. does a small boy sit B. sit a small boy C. did a small boy sit D. sat a small boy
A.
does a small boy sit
B.
sit a small boy
C.
did a small boy sit
D.
sat a small boy
【单选题】They arrived at the farmhouse, in front of which _________.
A.
is sitting a boy
B.
sat a boy
C.
a boy sat
D.
a boy is sitting
【单选题】We arrived at a farmhouse, in front of ______.
A.
it sat a small
B.
which a small boy sat there
C.
which sat a small boy
D.
it was a small boy
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