—You know，I’m poor in Chinese，you are not good  at English，and...

—That’s­­­­­     we should help each other.

A．what

B．when

C．where

D．how

变性蛋白质溶解度降低是因为蛋白质分子的电荷被中和，表面的水化膜被破坏引起的。