从A、B、C、D四个选项中，选出可以填入空白处的最佳选项，并在答题卡上将该项涂黑。
21．—How about ___________we go to the concert after dinner?
—Sounds a good idea!
A．when B．if C．whether D．that
22．—Who do you think will write to us, sister?
—I’m hoping to get ___________important letter from ___________father.
A．the;/ B．an; the C．an;/ D．the; the
