4 Essential Prime Implicants(EPI) which are A'C'D , ABC' , A'BC , ACD .
Remaining 5 Implicants are A'BD , BCD , BC'D , ABD & BD .
So, totally, there are 4 + 5 = 9 implicants. But 9 is not given in the options.
Actually, I marked option (A) 5 because there are 4 EPI and 1 implicant BD .
BD covers A'BD , BCD , BC'D , & ABD .