一道英语选择题，请详细说明理由

You should be always tell the truth.If you_________________,you will be in serious trouble.
A.will not
B.will not be back
C.would be back
D.am back

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句意 排除 CD 后面意思是你将会犯很大的错误
BCD中都有be back 猜出选B

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B 原意是否定的

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