We have made ______ great progress in the medical field, but ______ progress we have made is not enough.

[      ]

A. a; a

B. a; the

C. /; the

D. /; /

台风是发生在热带海洋上的一种具有暖心结构的气旋性涡旋，是达到一种强度的热带气旋。