题目：
I think the most helpful invention is light bulb. It seeing in the dark, and it gives people more time to work and play every day.
A. used to B. is used to C. is used for
答案：
答案：C
题目分析： used to过去经常做，但是现在不做了。be used to被用来做某事，后接动词原形。be used for用于做某事，后接动词ing形式。句意：我认为最有用的发明是电灯，它被用来在黑暗中看东西，这给人们带来了更多的时间去工作和娱乐。
