half－mast (半旗)．

　　解析：句意：一位游客向一个外国人解释为什么降半旗。根据主句谓语可知应用过去时。

　　4．We were told that there __was__(be)going to be an English corner in the hall at 7 o'clock p．m..

　　解析：句意：有人告诉我们下午七点在大厅有一个英语角。主句为一般过去时，在间接引语中，要用过去时态。而且an English corner为单数，因此用was going to be。

　　5．He asked, "When did Cambodia's former King pass away？" →He asked when Cambodia's former King __had_passed__ away.

　　解析：句意：他问柬埔寨前国王是何时去世的。直接引语是一般过去时，变为间接引语时要变成过去完成时。

　　6．He said，"Mother, the boy is very naughty." →He __told__ his mother that the boy was very naughty.

　　解析：句意：他跟妈妈说那个男孩很淘气。陈述句变间接引语时，主句动词可以用tell。

　　7．He told us last night that the flight to Shanghai __takes__(take) off at eight tomorrow.

　　解析：句意：昨晚他告诉我们到上海的航班明天八点起飞。直接引语表达的为客观现象，为时刻表规定的内容，变为间接引语时谓语动词需用一般现在时。

　　8．The head teacher told us that most of the students __were__(be) born in the 1990s.

　　解析：有具体的过去时间作状语的直接引语变为间接引语时，时态不变，仍然用一般过去时。

　　9．"Did the cold weather really begin？" the child said to his mother.→The child asked his mother __whether/if__ the cold weather had really begun.

　　解析：句意：孩子问妈妈寒冷的天气是否已真正开始。变间接引语时一般疑问句变为whether/if引导的宾语从句。

10．A spokesman said the other day that the company __had_said__(say