1. That's_________ used car which is often used__________ Mr. Grey.

A. an; by             B. a; by            

C. an; with         D. a; with

2. I wonder________ the machine without any help that day.

A. how did he mend                     

B. how he mends

C. how he mended                      

D. how does he mend

3.If H2 burns in O2 ,we can get _________

A. H2                B. H2O               

C. O2                D. H2O2