The correct answers are:
a. both coefficients are perfect squares.; and b. there are only two terms.
Step-by-step explanation:
In order to have a difference of squares, we will have only two terms. Algebraically, this can be represented by a²-b². This is by definition.
Since this is the difference of squares, both terms must be perfect squares. If they are not, then it is no longer the difference of squares.