I have two daughters and one son. They are Mary. Laura and Eric. Mary is seven. Laura and Eric are five. They watch a lot of television, maybe five hours a day.

    I'm worried that it's too much. Should I limit（限制） their screen time?

Catherine

    The American Academy of Pediatrics（APP，美国科学会） says that older kids shouldn't watch more than1-2 hours of television every day, and that kids under the age of two should not watch any television. The shows kids watch should be educational. All in all, television shouldn't be a substitute（替代物）for activities like playing with friends, exercising or reading.

    It was 8:30 at night. Don was driving home. He was surprised when he saw a large, green light in the sky. The light was floating（漂浮）over a field. Don stopped his car and went out. He stood behind a tree and watched.

    The light got very bright. It came nearer and nearer. It was a UFO! And it landed in the field!

    "What's that? Maybe there are travelers from space in the UFO, "he thought. He started to walk across the field.

    Then a large door on the UFO opened. Something came out! It moved toward Don.

    The thing was not nice to look at! It had long yellow strings（细绳）on its face. Two round and blue balls were on its face. Under the round things, there were three holes. One hole opened and closed and made big noises.

    Now Don was afraid, but he tried to be brave. He walked nearer and listened to the terrible noises.

    "Hello," said the strange thing. "My name is Zeeb. I'm from the planet Mars（火星）. This is my first trip to the earth. Glad to meet you."

    Mary and Peter were having a picnic with some friends near a river when Mary shouted, "Look! That's a spaceship up there and it's going to land here. "

    Frightened by the strange spaceship, all the young people got into their cars and drove away as quickly as possible except Peter and Mary. They were more curious（好奇的）than frightened. They watched the spaceship land and saw a door open, but nobody came out, so they went to look into it. In the centre of the floor, there was a lot of food. Peter followed Mary into the spaceship and did not hear the door close behind him. The temperature fell in no time and very soon the two young people didn't know anything.

    When they came to, they were surprised to see that they were back by the river again. The spaceship had gone. Their car was nearby.

    "What happened?" asked Mary.

    Peter scratched（搔）his head, saying slowly, "Don't ask me. Perhaps we had a problem. Come on. It's time to go home."

    After driving about fifty metres, they found a thick wall made of something like glass stood in their way. On the other side of the wall, a few strange aliens were looking through the wall and reading a notice, which translated into（译成）English said, "New comers at the zoo, a pair of earth villagers in their house on wheels. "