Trisha's three young children frequently argue and fight. to reduce this problem behavior, trisha sets an appropriate time limit during play time, and if the children refrain from squabbling during that period, they are immediately given positive reinforcement. according to the in focus box, "changing the behavior of others," this strategy is called:

The fact that Trisha sets an appropriate time limit during play time, and if the children refrain from squabbling during that period, they are immediately given positive reinforcement means that Trisha is using the strategy called: reinforcing the nonoccurrence of the problem behavior.
This strategy is an effective method to eliminate behaviors that might be troublesome in the classroom. 

The answer is to spread the world of christ