问题补充：
I’m good old people and I’m good playing the guitar, so I can join you to help them.
A. for, with
B. for, at
C. with, at
D. at, for
答案：
A. for, with
B. for, at
(答案→)C. with, at
D. at, for
解析：句意：我善于和老人打交道，我吉他弹得很好， 所以，我能加入和你们一起帮助他们。be good with sb善于与某人交往，be good at doing sth擅长于做某事，故选C
