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【单选题】
有机物一般不导电、难溶于水，其化学反应速度一般比较慢，同时常伴有副反应。它具有这些特点的根本原因是（）。A.
有机物分子较大
B.
碳元素不易氧化
C.
有机物中有氢键存在
D.
有机物中原子以共价键相结合
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皮皮学刷刷变学霸
举一反三
【单选题】下列哪项是生物素-亲和素系统放大作用的主要机制？( )
A.
经化学修饰生物素成为活化生物素
B.
亲和素的四个生物素部位，可同时结合多价性的生物素化衍生物
C.
两者之间极高的亲和力
D.
生物素、亲和素可分别与酶、放射性核素等结合形成标志物
E.
以上均不是
【简答题】简述钢屋盖结构屋面支撑的种类。
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【简答题】已知四阶行列式 D 中第三列的元素依次为 -1,2,0,1 . (1) 如果 D 的第三列元素的余子式依次为 5,3,-7,4, 则 D= (2) 如果第四列元素的余子式依次为 5,a,-7,4 , 则 a=
【单选题】She ______ someone, so I nodded to her and went away.
A.
phoned
B.
had phoned
C.
was phoning
D.
has phoned
【单选题】He went to the boy, and _______ him on the shoulder, took him away.
A.
pat
B.
patting
C.
patted
D.
to pat
【单选题】I wanted to have a talk with her, but she ______ me and went away.
A.
upset
B.
calmed
C.
ignored
D.
set
【简答题】阅读理解。 It was Sunday morning. Tom and his friend Dick went to the river to go fishing. Tom took his dog Tim with him.The dog usually sat quietly on the river bank.But sometimes when he saw a small anim...
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