Answer:
Option B=> Her mother accidentally drops a towel over the ball Mercedes is playing with.
Step-by-step explanation:
Object permanence abilities is one of the abilities that Psychologists use in tests how the development of human beings are especially in children. Object permanence abilities actually deals with children having pictures of something in their brain for instance now, when a child actually knows that he or she has an object that he/she can play with, although the child may not be able to find it(maybe the parent has kept the object) buy the child still believes that the object is still in existence and thus, he or she will continue looking for it until it is found.
So, back to the question, Mercedes will be looking for the ball despite the fact that it is hidden from her, she will still believe that she has a ball and continue searching for that ball.