The waterfall_______the rocks.

A．not to judge a egg by its shell
B．not to judge a person's intelligence by his appearance
C．not to make the mistake of thinking a young man stupid
D．not to overestimate a student's intelligence

A．a good writer is always a good speaker
B．a good writer may not be a good speaker
C．a good writer will find himself speechless
D．a speechless person always writes well