3 is always on the numerator. It is not effected by a power. The answer has to be something that leaves the numerator alone. That means that B is not correct.
The answer is going to be something that makes the denominator 1 when n = 1. That's going to be the answer to the question, because the first term in the sequence is just 3. The denominator must be 1. (not zero).
D is not the answer, because 3/5^1 = 3/5, so D is wrong.
A is not going to get us anywhere either. 3/5^(1 + 1) = 3/5^2 = 3/25 which is not the first term.
The only choice we have left is C. It must be the answer. 3/5^(1 - 1) = 3/5^0 = 3/1 = 3. There's your answer. Note anything raised to the zero power = 1.