单选题：I always take something to read when I go to the doctor's _..

___ he made up his mind, nothing could change it. [ ]A. BeforeB. Unless C. When D. Once

—Did you catch the early bus this morning?—No.It had left the stop _____ I arrived there.[ ]A. as soon asB. as the timeC. by the timeD. during the time

She had just finished her homework _____her mother asked her to practice playing the piano yesterday. [ ]A. when B. while C. after D. since

— Can you describe _____it happened?— Yes,I was riding on my bike_____ a car knocked me down from behind. [ ]A. when; as B. how; asC. how; when D. how; while

I can still remember, ________it was so long ago.[ ]A. ever sinceB. now thatC. even thoughD. even as