have you found out the telephone number I need?yes,but____,I have sat here for nearly a half hou

题目

have you found out the telephone number I need?yes,but____,I have sat here for nearly a half hou
Have you found out the telephone number I need?
Yes,but____,I have sat here for nearly a half hour.
A.for finding it out B to find it out
请问A为什么不行?

答案

to do sth 表示目的
这句话是说、为了找到它、我已经在这坐了半个小时了