什么词在句中不担任句子成分
一般说来，虚词在句中不可以单独担任句子成分。
1、冠词：置于名词之前
The boss and his secretary are flying to
It was an agreement the details of which could not be altered. 这是一项其细节不可更改的协定。
Her birthday is next Monday, so I must buy her a present. 她的过生日就在下星期一，所以我需要给她买一件礼物。
2、介词：一般也置于名词之前
The Japanese admire the traditions of the Chinese. 日本人羡慕中国人的传统。
If you get into difficulties, Monica is the person to ask. 你如陷入困境，只去找莫尼卡即可。
A doctor examined the astronauts. They returned from space today. 大夫给宇航员们进行了检查。他们今天从太空返回。
3、连词：置于词与词、短语与短语、从句与从句与分句与分句之间，或置于从句之首
The dispute will end if and when both sides agree. 只有在双方达到协议时，辩论才会结束。
We came home after our holiday to, find our garden neat and tidy. 大家度假归来发现大家的花园干净而且整齐。
She drew the curtain back, and the room was flooded with gold. 她拉开窗帘，房间里立即充满金色的阳光。
注意：虚词与其他词构成短语，则可以担任句子成分，如介词与名词、代词、动名词等构成介词短语则可以担任句子成分。
