Read the following passage and mark the letter A, B, C, D on your answer sheet to indicate the best answer to each of the following questions from 4 to 6.

[I] Do you find yourself yawning all day at school? You probably need more sleep. [II] However, it is not just how much sleep you get that is important. [III] What you do before bedtime also has a huge effect on how you feel the next day. [IV] If you spend time chatting to someone on social media, or reading a book on your e-reader, you are not alone.

All devices’ screens give out a large amount of blue light, which affects the body’s production of the sleep hormone, melatonin, which can change your sleep patterns. So it is not just getting to sleep that becomes hard, but the quality of your sleep also suffers. The result is that you can wake up several times during the night, and have difficulty getting up in the morning.

Sleep is food for the brain, so not sleeping well can be a severe problem for anyone, especially for teenagers, because their brains are still developing. When you do not sleep well, it can be difficult to concentrate at school, which makes it harder to learn and get good grades. It can also affect your mood, making you feel sad or anxious.

So, it is clear you should not use your phone before you go to sleep. Why not leave it in another room? Nothing on social media is so important that it cannot wait a few hours! You should rediscover paper books and enjoy feeling tired and sleepy before bedtime rather than wondering why your best friend has not liked your photo! How will you wake up? You do not have to use the alarm on your phone. Go and buy yourself an old-fashioned alarm clock! The negative effects that screen time is having on sleep have been in the news a lot recently, so manufacturers of smartphones and tablets have added a feature to the mobile devices that can help reduce these. Most new phones have a night-time setting that changes the colour of the screen so that it gives out less blue light. If you really cannot avoid going onto social media at bedtime, think about turning on this setting on your phone.

The word trigger in paragraph 2 could best be replaced by ______.