Has been smoked ??

“The part of a cigarette that is left after it has been smoked.”
The above sentence is not a complete sentence.
After removing “that”, it is a complete sentence.
“The part of a cigarette is left after it has been smoked.”

(1)
It has been smoked.
香煙(它)剛剛被抽過[被動式] [smoke的 present perfect tense ]
(2)
The part of a cigarette is left
煙頭被遺棄[被動式] [leave的 present tense]
(3)
after 在…之後
(4)
The part of a cigarette is left after it has been smoked.
在香煙剛剛被抽過之後煙頭被遺棄

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正確答案是cigarrete butt，不是cigarrete bud。

Left 是剩下，
After 是之後，
全句是：抽過的煙剩下的部份

2010-01-27 16:50:14 補充：
Sorry, there is a spelling mistake.

It should be
cigarette butt.

=煙頭 (食完支煙剩下的那部份...)
=cigarette bud(s)