Please someone explain me why the answer is not B (4k2m3)?

Hi there!
[tex]4k^2m^3[/tex] is definitely a factor of the the given terms. However, 4 is not the greatest common factor between 8 and 48; it is 8. Therefore, the GCF of the given terms would instead be [tex]8k^2m^3[/tex].
I hope this helps!