The reason most Chinese have healthy white teeth is they eat a healthy diet. A. why; tha

问题补充：

The reason most Chinese have healthy white teeth is they eat a healthy diet.

A. why; that

B. why; because

C. that; that

D. for; that

答案：

(答案→)A. why; that

B. why; because

C. that; that

D. for; that

解析：考查定语从句及名词性从句。句中why引导定语从句，先行词the reason在从句中作原因状语；that引导表语从句，故选A。