Assertion A: In complex real$-$world projects, it is common to use scheduling tools from Operations Research.

Reason R : Scheduling tools essentially take a hand constructed complete partial$-$order plan and generate an optimal schedule for it$.$

A$.$ Both A and R are true and R is the correct explanation for A

B$.$ Both A and R are true but R is not the correct explanation for A

C$.$ A is True but R is False

D$.$ A is false but R is True