从所给的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填涂黑。
21. ---How long are you staying?
---I don’t know. ________.
A. Everything is OK B. Never mind
C. It depends D. It doesn’t matter
22．In memory of China’s Youth’s Day, ____________ celebration evening took place on our campus. It was ___________ success.
A．a; a B．the; the C． a; / D．the; a
