I.单项填空。
( ) 1. When I got there, he ________ them to dance.
A. is teaching B. teaches C. taught D. was teaching
( )2. We were reading the newspaper _______ suddenly the light went out (熄灭).
A. when B. while C. as D. /
( )3. Mary was listening to music while she _________ to school.
A. walked B. was walking C. is walking D. walks
