第二部分：英语知识运用（共两节，满分45分）
第一节单项填空（共15小题；每小题1分，满分15分）
21. As we know, ______Potala Palace, a combination of Tibetan construction art and culture, is considered________precious treasure of China.

A．a; a

B．the; a

C．the; the

D．a; the