----Can you tell me live a low-carbon(低碳) life ?----OK. By using both sides of the paper.

问题补充：

----Can you tell me live a low-carbon(低碳) life ?

----OK. By using both sides of the paper.

A. where’s

B. why to

C. when to

D. how to

答案：

A. where’s

B. why to

C. when to

(答案→)D. how to

解析：where在哪儿；why为什么；when什么时候；how怎样。根据答语。好吧，把纸的两面都用了。表示通过某种方式，故选D。