One of the requirements for a fire is that the material______to its burning temperature（）
A. were heated
B. must be heated
C. is heated
D. be heated
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（）The noise of desks_______could be heard out in the street
A. opened and closed
B. to be opened and closed
C. being opened and closed
D. having been opened and closed
—I‘ve be en told to pay the rent.—But it‘s already been paid.It______by someone else（）
A. must be
B. may be
C. must be paid
D. must have been paid
Jimmy‘s mother went out because________（）
A. she waited for hours
B. nobody called
C. she had to buy some bread
D. she had to buy some milk
—I started to study，but then a friend called.—That‘s no excuse________（）
A. for not studying
B. not for studying
C. not studying
D. not to studying
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