Correct answer is A
An aggregate plan determines the aggregate production levels, inventory levels and resource capacities over the planning horizon. The resource capacities such as workforce levels are determined assuming one aggregate unit of production.
All other options are objective of Aggregate Production Planning whereas option (A), Scheduling of machines is the objective of detailed Job shop Scheduling/operations scheduling. This answers which machine will be used to produce which product/job and when the products/jobs will be produced.