问题补充：
Never protecting our earth. It is the only nice planet for us to live on.
A. leave for
B. learn about
C. give up
D. look up
答案：
A. leave for
B. learn about
(答案→)C. give up
D. look up
解析：句意:不要放弃保护我们的地球。对于我们来说只有一个星球可以居住。leave for 离开去某地；learn about 了解；give up 放弃；look up 查找。根据句意可知，这里让我们不要停止保护地球。give up doing sth. 放弃做某事。故选C。
