Many people believe that ______ will take years to develop a car that does not pollute the air. [ ]

A. it

B. that

C. there

D. this

治疗溃疡性结肠炎的有效药物是（）

A.克拉霉素

B.羟氨苄青霉素

C.柳氮磺吡啶

D.头孢曲松

E.氧氟沙星