— Could you tell me           ?

— Yes. To take back my dictionary. [ ]

A. why did you come here

B. when do you come here

C. why you came here

D. when you come here

目前造成城市空气中铅污染的主要来源是 [ ]

A．煤的燃烧

B．汽车废气

C．垃圾燃烧

D．废塑料燃烧