---Mr Wang, I have trouble ________ the text.

---I’m sure you can, but remember ________ it at least three times.

A．to understand; reading

B．understanding; reading

C．to understand; to read

D．understanding; to read

按照成因分类，湖流可以分为( )。

A．梯度流

B．惯性流

C．混合流

D．风成流