A:2
B:﹣2
C:±2
D:2
A
B
C
D
X
SO2
Cl2
HCl
NO2
Y
NaOH溶液
饱和NaCO3溶液
饱和NaCl溶液
Na2SO3溶液
By mentioning Muhammad Ali's words, the author intends to tell us that.