This is a complex sentence.

这是一个复杂的问题。

Is it a complex sentence?

是个复句吗？

Learning complex sentence structure.

复合句结构学习；

This is a compound-complex sentence.

这是一个并列关系的复句。

So any complex sentence just keep them together.

所以任何复杂句都能把他们合在一起。