Answer:
a. efficiency variances which indicate the need for corrective action.
Explanation:
Operational control basically relates to the operations of the business, price variance describes the rate at which material is acquired, it has no direct relation with operational control as relates to purchase of equipment.
Further, when talking about the efficiency variance it relates to production hours used in relation to standard hours, which help in maintaining operational control.
Therefore, correct option is:
a. efficiency variances which indicate the need for corrective action.