__ I made some foreign friends,I found English very useful.Before/After/So/If

问题描述:

__ I made some foreign friends,I found English very useful.
Before/After/So/If

肯定是After

It's not so late to find such thing.

after 在我交了一些外国朋友后 我发现 英语十分有用

after 我交了一些外国朋友之后,我发现非常有用的英语