下列各数互为相反数的是（　　）

A．3²与-2³

B．3²与（-3）²

C．3²与-3²

D．-3²与-（-3）²

A number of books in the library ___been stolen so that the number of them___ smaller than before.

A．have , is

B．has , is

C．has , are

D．have, are