— Can we leave the classroom now?

— No, you ______. You ______ to leave until the bell rings.

A．mustn’t, are allowed

B．don’t have to, are allowed

C．needn’t, aren’t allowed

D．can’t, aren’t allowed

A floating constant consists of an integer part，a decimal point，a fraction part，an e or E，and an optionally signed integer ．

A．exponent

B．order

C．superfluous

D．superior