How many combinations of three letters taken from letters (a, a, b, b, c, c, d) are possible?	Pick:	A) 12	B) 13	C) 35	D) 36	E) 56
Combinations only... total 13   So 4C3 for abcd - 4 choices   3 more for aa(b,c or d)   3 more for bb(a,c or d)   3 more for cc(a,b or d)   total 13   (Answer 13)
<result>B</result>
How many combinations of three letters taken from letters (a, a, b, b, c, c, d) are possible?