【GMAT数】all of the following have the same number of distinct

【GMAT数】all of the following have the same number of distinct prime factors except:20,21,24,30,45【GMAT数学】all of the following have the same number of distinct prime factors except:(A)20(B)21(C)24(D)30(E)45,答案为什么是D我的理解：20=2*2*5,21=3*7,24=2*2*2*3,30=2*3*5,45=3*3*5,21,24,30,45的公因数3相同,所以选A,我错在哪儿?