问题补充：
The poor girlacross the roada car knocked her down.
A. walked; while
B. walked; since
C. was walking; until
D. was walking; when
答案：
A. walked; while
B. walked; since
C. was walking; until
(答案→)D. was walking; when
解析：根据时间状语从句，从句的动作发生在主句动作之中，主句用进行时，而从句用一般过去时，故选D
