—The number of the students in our class fifty-six.
—How many of are girls?
A:is; them
B:are; them
C:is; they
D:are; they
向NaCl、NaOH和Na2SO4三种溶液中,分别加入不同物质,通过一步反应都能生成化合物M,则M是( )
某溶液中含有Cl﹣、CO32﹣、HCO3﹣等3种阴离子,如果只取一次该溶液就能够分别将3种阴离子依次检验出来,下列实验操作顺序正确的是( )
①滴加Ca(NO3)2溶液;②过滤;③滴加AgNO3溶液;④滴加HNO3溶液.