If you choose to play a video game instead of reading, your opportunity cost would be to read a book. Factories make goods to send to stores to be sold. The grocery store shelves are filled with jam, cereal, and baby food we need at home. When goods are produced on an assembly line, someone checks for the quality of the product. Most goods go through a quality inspection before being sold in stores.
Dolls even get a quality check.
Boys and girls use resources like desks, books, globes, and computers at school. They use desks for doing work and books, globes, and computers for learning. A librarian gives us service by helping us find the books we want in the library. We do not have to pay her for this community service. Other services we have to pay for, like full service at some gas stations.