Answer:
Second and third option
Explanation:
The denominator is always what a is being rooted by, and the numerator is the exponent of a.
The first one shows this as b is the exponent of a, and a is being rooted
by c
The second one also shows this by having c rooting a, and even though b is not directly the exponent of a, as it is on the outside now, but it is still the same thing and counts.