Yes, you can do that.
The only downside with that strategy (testing values) is that you can never be 100% sure of the correct answer UNLESS you find two conflicting cases (which means the correct answer is D).

For example, if 2^p + 4^q, then one possibility is that p = 0 and q = 0
In this case, p = 2q

Another possibility is that p = 2 and q = 1
In this case, p = 2q

Another possibility is that p = 4 and q = 2
In this case, p = 2q

Another possibility is that p = 6 and q = 3
In this case, p = 2q

At this point, it certainly SEEMS like the correct answer is C.
But, perhaps there's a pair of values that we haven't checked yet and those values would show that p ≠ 2q

Although the correct answer is, indeed, C, we can't be 100% sure of that when we test values.

I discuss those limitations in the following video (starting at 2:50)


Cheers,
Brent