---Can you tell me why you learn English so well ?-It is very simpleyou work grade

问题补充：

---Can you tell me why you learn English so well ?

---It is very simple. you work, grades you will get.

A. The harder: the best

B. The hard: the better

C. Harder: better

D. The harder: the better

答案：

A. The harder: the best

B. The hard: the better

C. Harder: better

(答案→)D. The harder: the better

解析：句意:能告诉我你为什么学英语学得这么好吗？很简单。你学习越努力，你取得的成绩就越好。The+比较级---，the+比较级---，意思为越------就越------。结合语境可知选D。