— Is this your school?
— .
A:Yes, it isn't
B:No, it is
C:Yes, it is
D:No, this isn't
设NA表示阿伏加德罗常数,下列叙述中正确的是( )
已知a+b=-5,ab=3,则a2+b2的值为 ( )
食品安全是关系到我们健康的大事,下列做法不正确的是( )