There were so many kinds of toy cars that I couldn't decide ________.

1. A.
   what to buy
2. B.
   which one to buy
3. C.
   to buy which one
4. D.
   which one should buy

There were so many kinds of toy cars that I couldn't decide ________.

[　　]

A．what to buy

B．which one to buy

C．to buy which one

D．which one should buy