G={1,2,3,4,5,6},⊕7
(a) {2,6,1) is not a subgroup ∵2⊕76=5∈/{2,6,1}
(b) {1,2,4} is a subgroup ∵ it satisfies all properties of group. 1⊕72=2,2⊕74=1,4⊕71=4
(c) {5,4,2} is not a subgroup · ∵ In this set identity element do not exist.
(d) {2,3,1} is not a subgroup ∵2⊕73=6∈/{2,3,1}