In no circumstance __________ .
A. smoking should be allowed on the campus
B. should smoking b allowed on the campus
C. should smoking allowed on the campus
D. should smoking allow on the campus
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原胶原肽链的一级结构具有重复排列的三肽序列，其三肽序列中的第一个氨基酸残基几乎总是()。
A. 脯氨酸
B. 赖氨酸
C. 甘氨酸
D. 亮氨酸
Although Jack made a foolish mistake, we __________ at him
A. ought to have laughed
B. oughtn’t to have laughed
C. ought to laugh
D. should not to laugh
动物细胞间的物质交流和信息传递是通过何种连接方式实现的？()
A. 中间连接
B. 间隙连接
C. 桥粒
D. 紧密连接
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