第一节：单项填空（共15小题；每小题1分，满分15分）
从A、B、C、D四个选项中，选出可以填入空白处的最佳选项。
21. It’s the second time that I _______ in Beijing. What great changes! It’s years since I ________ here last time.
A．went; had left B．had been; left C．have been; left D．have; had left
22. People from all over the world ________ China on the successful launch of Chang’E-1.
A．celebrated B．greeted C．congratulated D．enjoyed
