选择填空。

— Are those your tennis rackets?

— No, ______. [ ]

A. it isn't

B. they are

C. those aren't

D. they aren't

人防工程必须使用（）生产的防护专用设备设施，并在土建施工时实施安装。

A.国家定点企业

B.省定点企业

C.省认可企业