Read the text and answer the question.

Many people today can’t imagine their lives without gadgets. If we don’t have our smartphones with us, we feel lost. Gadgets help us stay in touch, do our work, and even entertain ourselves. If you use a phone late at night, you won’t sleep well. Also, if a child spends too much time playing on a tablet, he often becomes tired and unfocused.
Some people believe that if you use smartwatches, they help you stay healthy. For example, if you walk a lot during the day, your watch shows how many steps you’ve taken. If your gadget breaks, you can usually get it repaired or replaced. But if you don’t look after it, it won’t last long.

Why can children become tired, according to the text?

• because they watch TV
• because they don’t eat
• because they use tablets for too long
• because they go to school