The teacher told us that light travels at a very high speed.
（2）主语从句作主语相当于单数第三人称作主语，谓语动词用单数，如果由and 连接两个或两个以上的主语从句作主语时，谓语动词用复数；由两个或多个连接词引导一个主语从句，谓语动词用单数。如：
When the meeting will begin has not been decided yet.
When they will start and where they go have not been decided yet.
When and where the meeting will begin has not been decided.
3、名词性从句的词序
名词性从句在句中要用陈述句语序。如：
He asked me what was the matter with me.
We’ve heard the news that we’ll move into the new house.
Whatever you say will interest us all.
二、精典名题导解
选择填空
1. A computer can only do ________ you have instructed it to do.
A.how B.after C.what D.when
解析：答案为C.本题考查的是名词性从句作宾语的用法。此句的引导词既作连词又在宾语从句中充当一成分，故what最合适。
2. —I drove to Zhuhai for the air show last week.。
—Is that _________ you had a few days off
A.why B.when C.what D.where
解析：答案为A.此题考查的是从句的用法。根据题意“我上周开车去珠海看航空展去了。”下面一句接着问：“那就是你为什么离开的原因吗？”故用why引导表语从句表示原因。
3. I hate __________ when peope talk with their mouths full.
A.it B.that C.these D.them
解析：答案为A.本题考查的是形式宾语的用法。题意为“我讨厌人们谈话时嘴里塞满东西”。该空白处没有任何含义，而且已经用了when连接该宾语从句，所以此处只填一个形式宾语it.