It was _____ terrible earthquake and ______ number of people who were killed reached more than 20,000.

A．a; the

B．the; a

C．the; the

D．a; a

草履虫是单细胞生物，但同样有呼吸、取食等新陈代谢活动。实验时用吸管从草履虫培养液中吸取草履虫，最好的部位是（）

A.培养液的表层

B.培养液的中层

C.培养液的下层

D.培养液的任一部位