根据句意及汉语提示，填写单词。

1. I saw Jack sitting _____ (在……旁边) Jim talking.

2. I don't understand the meaning of this _____ (符号).

3. My sister got the answer to the _____ (谜语) very quickly.

4. Many people are against _____ (做实验) on animals.

5. He gave me a _____ (恰当的) example, so I understood it easily.

To be ______ changing times you cannot have your body in the 21st century and your head back in the past.

A．in step with

B．in front of

C．together with

D．apart from