I personally think__more listening, speaking, reading and writing is the key to__our English.

A. Doing; improve   B. To do; improve     C. Do; improving    D. Doing; improving

I personally think__more listening, speaking, reading and writing is the key to__our English.

1. A.
   Doing; improve
2. B.
   To do; improve
3. C.
   Do; improving
4. D.
   Doing; improving

I personally think__more listening, speaking, reading and writing is the key to__our English.