Passage ThreeFor more than six million American children, coming home after school means coming home to an empty house. They spend part of each day alone. They are called "latchkey children". They're children who look after themselves while their parents work. And their bad conditions have become a social problem.Lyne Brown was once the headmaster of an elementary school. She said, "A lot of kids had chains around their necks with keys attached.! was constantly telling them to put them inside shirts. There were so many keys, it never came to my mind what they meant. ",slowly, she learned they were house keys.Lyne learned of the impact working couples and single parents were having on their children. She found that Fear is the biggest problem faced by children at home alone. Many had nightmares and were worried about their own safety.The most common way latchkey children deal with their fears is by hiding. It might be in a shower stall, under a bed, in a closet. The second is TV. They'll often play it at high volume. It's hard to get statistics (情况，材料) on latchkey children. Most parents are slow to admit they leave their children alone.41. The main idea about "latchkey children" is that they______.