.---You see, I’m not good at English, you are poor in maths, and…

  --- That’s _______ we’d better help each other.

A. when               B. how                 C. why                    D.what

—You see，I’m poor in maths，you are not good at English，and...
—That’s________we should help each other.

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

—That’s________we should help each other.

A．when            B．where            C．how              D．what

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

—That’s________we should help each other.

A．when      B．where     C．how     D．what

---You see，I'm poor in maths，you are not good at English，and．．．

---That's ________ we should help each other．

1. A.
   when
2. B.
   where
3. C.
   how
4. D.
   what