（1）賓語(yǔ)從句中主句和從句的時(shí)態(tài)保持一致，但如果從句中表示提示的是客觀現(xiàn)象，雖然主句是過(guò)去時(shí)態(tài)，從句仍用一般現(xiàn)在時(shí)。如：
Hello,I didn’t know you were in London. How long have you been here?
The teacher told us that light travels at a very high speed.
（2）主語(yǔ)從句作主語(yǔ)相當(dāng)于單數(shù)第三人稱作主語(yǔ)，謂語(yǔ)動(dòng)詞用單數(shù)，如果由and 連接兩個(gè)或兩個(gè)以上的主語(yǔ)從句作主語(yǔ)時(shí)，謂語(yǔ)動(dòng)詞用復(fù)數(shù)；由兩個(gè)或多個(gè)連接詞引導(dǎo)一個(gè)主語(yǔ)從句，謂語(yǔ)動(dòng)詞用單數(shù)。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.
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