When you finish reading the book you will have better understanding of life. 　A. a; theB

问题补充：

When you finish reading the book, you will have better understanding of life.

A. a; the

B. the; a

C. 不填; the

D. a; 不填

答案：

A. a; the

B. the; a

C. 不填; the

(答案→)D. a; 不填

解析：表示对某东西有所了解时，习惯在understanding前加不定冠词；而life泛指生活时，前面不用任何冠词。