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[主观题]
Which of the following is not a correct understanding about the word "extra" in giving a t
ip?
A.Extra is a fixed charge in some cities.
B.Extra is similar to a tip in some cases.
C.If the "extra" is paid, one doesn't tip any more.
D.Some hotels require people to pay an "extra" service charge.
![](https://lstatic.shangxueba.com/sxbzda/h5/images/tips_org.png)