In sub-saharan africa, female genital mutilation is
a. most common in northern countries of the region.
b. unheard of in central africa and namibia.
c. rare in mali.
d. uncommon in nigeria.

C - definitely not the case, it's very common in Mali
B - also not the case, it's not very common but it's not "unheard of"

As for A and D, it's problematic.
A - hm, this is also not really true, it would be better to call it that it's more common in the east and West and less common in the center
D- In Nigeria 25% of women undergo it, and it also recently banned it - it's not little and it's not "uncommon" but it's less than in other contries in teh region.

so both A and D are partially true, partially false, but I think that A is better than D because  the some of the countries where FMG is most present, Mali and Egypt, are in the north and the southern counties have it less.