选 A .
时间介词用at: at 10 o'clock
日子介词用on: on monday
时间的用法：两点半：two thirty 或者thirtypast two或者thirty to three
超过多少点用past差多少到几点用to.
差15分钟3点(2:45)：one quarter to three.
3点15：one quarter past three.