二、单项选择题：阅读下列各题，从题后所给的A、B、C、D四个选项中选择一个最佳答案。(20小题，每小题1分，共20分)
21. There's _________800-metre-long road behind _________hospital.
A.an,an B.a, a C.an, the D.a, the
22. The population of the world ____ still ____ now.
A.has; grown B.is; growing C.will; grow D.is; grown
