Given below are two statements, one is labelled as Assertion (A) and the other is labelled as Reason (R):
Assertion (A) According to the first theorem of welfare economics, a competitive equilibrium is Pareto efficient.
Reason (R) : According to the Walras law, the value of aggregate excess demand is zero for all prices.
In the light of the above statements, choose the correct answer from the options given below: