1. Set X is what of Set Y if all elements of X are also elements of Y ?
A. complement
B. intersection
C. proper subset
D. subset​
2. if set A composed of 3, 6, 9 and set Y is composed of 6 and 9, then set Y is what of set A?
A. complement
B. intersection
C. proper subset
D. subset
3. what is the cardinality of the given set, {-3, -2, -1, 0, 1, 2, 3}?
A. -3
B. 2
C. 3
D. 7