B1: ({0, 1, 2 .(n-1)}, xm) where xn stands for multiplication-modulo-n and B2: ({0, 1, 2 .n}, xn) where xn stands for multiplication-modulo-m are the two statements. Both B1 and B2 are considered to be __________

B1: ({0, 1, 2 .(n-1)}, xm) where xn stands for multiplication-modulo-

1.	B1: ({0, 1, 2 .(n-1)}, xm) where xn stands for multiplication-modulo-n and B2: ({0, 1, 2 .n}, xn) where xn stands for multiplication-modulo-m are the two statements. Both B1 and B2 are considered to be __________
A.	groups
B.	semigroups
C.	subgroups
D.	associative subgroup
Answer» C. subgroups