-Which tie is more suitable for me, the red one or blue one?

-I have no idea. You'd better take them __________.[ ]

A. all

B. each

C. every

D. both

下列叙述正确的是（　　）

A．含有共价键的化合物一定是共价物

B．气态单质分子中一定存在共价键

C．共价化合物中一定存在共价键

D．离子化合物中只含有离子键