A portfolio comprising a long call and a short put option has the same payoff...

To answer this question, we need to look at the put-call parity, which can be expressed as:

Value of call - Value of put = Spot price - Exercise price discounted to the present

or, Value of call - Value of put = Stock - Bond with a future value equal to exercise price

Therefore, a long call and a short put is equivalent to a long stock position and a short bond.

Choice 'a' is therefore the correct answer. (Alternatively, we could also have constructed a graph of the payoff profiles to arrive at the same answer).