a)

. The square power of an odd integer is always an odd integer. For example:

b)

.

is an even integer and

is an odd integer. The difference between both numbers is and odd integer.
c) The product of an even integer (2a) and an odd integer is always a
even integer.
d) The product of an even integer (a) and other even integer (2b) is always a
even integer.
The answer is c) and d) cases.