Clifford's Lawn Work Is Steady and Up to Standard as Long

Clifford's lawn work is steady and up to standard as long as his work is verbally praised approximately every twelfth completed mower circuit. However, at times the crew chief is unable to praise his work at that moment. When praise is not forthcoming, Clifford usually stops working. The best way to facilitate maintenance and generalization of Clifford's work, using a self-management technique, would be to:

A) have fellow workers provide praise when Clifford stops working.
B) have the crew chief use a variable schedule of reinforcement.
C) increase the delay in reinforcement until the afternoon.
D) teach Clifford how to request reinforcement for the target behavior.