This question is very difficult I ask my brother for help.A. butB. or C. becauseD. so

问题补充：

This question is very difficult I ask my brother for help.

A. but

B. or

C. because

D. so

答案：

A. but

B. or

C. because

(答案→)D. so

解析：句意：这个问题是非常难的，所以我请求我的哥哥帮忙。A. but但是； B. or或者； C. because因为；D. so所以。结合句意，前半句表示原因，因为题太难，后半句表示结果，所以我请求哥哥帮忙。故选D。