从各题所给A、B、C三个选项中，找出和画线部分意思相同或相近并能替换画线部分的选项。

1. He worked out the math problem in the end.

A. at last

B. at the end

C. final

2. Please give up smoking.

A. stop to smoke

B. stop smoking

C. go on smoking

3. If he is tired, he can stay at home and relax himself.

A. drink some water

B. have a rest

C. work on

4. We should do our best to improve the environment.

A. keep the environment

B. make the environment worse

C. make the environment better

5. The Smiths will return home next week.

A. give back

B. get back to

C. get back