They develop their skills they can do things better and better.A. howeverB. becauseC. sin

问题补充：

They develop their skills they can do things better and better.

A. however

B. because

C. since

D. so that

答案：

A. however

B. because

C. since

(答案→)D. so that

解析：状语从句。句意：他们拓展他们的技能是为了他们能够把事情做的越来越好。后面的从句表示目的，只有D符合题意。