— ___________________

— Once or twice a week.

A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.

11.张骞出使西域开辟丝绸之路之时，与汉朝同时的还有_____、______、______、______和笈多王朝等强大国家。

15.史书上确切记载的丝绸之路是汉武帝时_____出使西域所开辟的丝绸之路。