— Did you listen to the program yesterday?
— Yes. I can't believe I heard her singing ______ the radio.
A:on
B:in
C:by
D: For
实验编号
HA物质的量浓度
(mol•L﹣1)
NaOH物质的量浓度
混合溶液的pH
甲
0.2
pH=a
乙
c
pH=7
丙
0.1
pH>7
丁
pH=9
____
我国规定对12岁以下儿童实施“四苗”常规接种,进行预防接种的目的是( )