二、单项选择(15小题，每小题l分，共l5分)
从A、B、C、D四个选项中选出—个最佳答案，并将其标号填入答题卡相应位置。
21．
一 Jerry，you made _______mistake here!
一 Really ? Oh，yes．I missed_ _______“I” in the word “challenge”．
A．a，a B．a，an C．the，an D．the，a
22．_______the morning of February 27，millions of basketball fans enjoyed a fantastic performance，2012’s NBA All-Star Game．
A．For B．At C．In D．On
