几种DNA分子的碱基组成比例如下，DNA的Tm值最低的是A．A+T=70% B．G+

I shall never forget the days _____ I spent in Beijing University, _____ has a great effect on my life. [ ]

A. that; which

B. which; that

C. when; that

D. when; which

Come and see me whenever ____.

A．you are convenient

B．you will be convenient

C．it is convenient to you

D．it was convenient to you

教育与自我教育。

据《安全生产法》规定，安全生产社会中介机构弄虚作假出具假证明的，由安全生产监督管理部门吊销其资格证，没收违法所得，并处______万元的罚款。

A．1～2

B．3～5

C．6～9

D．10以上

退休