病毒的基本结构指的是（）
A.DNA和包膜
B.DNA和RNA
C.RNA和衣壳
D.核心和包膜
E.核心和衣壳
参考答案：E
Though Professor Liu ____ in New York for seven years, he has never regretted moving back to Shanghai, his hometown.
A．lived
B．has lived
C．had lived
D．was living
Visual FoxPro 6.0属于（ ）。
A．19
B．3
C．11
D．7
