What Do Researchers Mean When They Describe Play as a "Serious

What do researchers mean when they describe play as a "serious business"?

A) Play is not as much fun for children as it appears to an adult observer.
B) Unsupervised play has serious negative outcomes for intellectual and social development and should be discouraged.
C) Play has significant positive effects on a child's social and intellectual development and should be encouraged.
D) All children's play should be directed and controlled by adults.