下列战役，发生于抗日战争相持阶段的是
①淞沪会战 ②徐州会战 ③百团大战 ④豫湘桂战役 [ ]
A．①②
B．②③
C．①④
D．③④
答案：D
.
— When did they come back last night?
— It was midnight ____ all of us were sleeping.
A．that
B．when
C．which
D．in which
控制病毒遗传变异的病毒成分为（）。
A.包膜蛋白
B.核酸
C.病毒衣壳
D.脂质成分
E.病毒酶
