Option a:
is the correct answer.
Explanation:
The expression is 
We shall simplify the expression, to determine the expression which is equivalent to 
Multiplying the powers, we get,

Again multiplying the powers, we get,

Dividing the fractions, we have,

Applying the exponent rule,
, we have,

Hence, the expression can be written as

Thus, the expression which is equivalent to
is 
Hence, Option a is the correct answer.