两个轻小物体相互吸引，则：[ ]
A．两个物体必定带同种电荷
B．两个物体必定带异种电荷
C．两个物体都不带电
D．两个物体中至少有一个带电
答案：D
Where were you at supper time? I _____ for you to join me. [ ]
A. waited
B. had waited
C. have been waiting
D. was waiting
细胞融合有利于病毒的（）。
A.复制
B.吸附
C.扩散
D.脱壳
E.释放
