unless  副詞連接詞     如果不，除非.

I won't apologize unless she apologizes first.

I will have this egg unless you want it.

S + V  unless  S + V

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The personnel manager makes it clear that for security reasons, no one is allowed to enter the building _______ presenting a photo ID card.

A)unless

B)without

C)because

D)if

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(B).

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