OG上面的一道题，很费解（NN请进！）

if the positive integer x is a multiple of 4 and the positive integer y is a multiple of 6,

then xy must be a multiple of which  of the following ?(yellow book Page23)

I     8

II   12

III   18

the solution provided by OG is  I and II only , which makes me complicated.

give me some guide, please!!!!

thanks, ptr07 and  hohoo

i understand now！