In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.

Example input: Article: Homework can put you in a badmood , and that might actually be a good thing. Researchers from the University of Plymouth in England doubted whether mood might affect the way kids learn. To find out the answer, they did two experiments with children. The first experiment tested 30 kids. Someshapes were hidden inside a different, larger picture. The kids had to find the small shapes while sitting in a room with either cheerful or sad music playing in the background. To test their mood, the scientists asked the kids to point to one of five faces, from happy to sad. Children who listened to cheerful music tended to point to the smiley faces while the others pointed to the unhappy ones. The researchers found that sad kids took at least a second less to find the small shapes. They also found an average of three or four more shapes. In the second experiment, 61 children watched one of two scenes from a film. One scene was happy, and the other was sad. Just like in the first experiment, kids who saw the sad scene acted better compared to the others. The researchers guessed that feeling down makes people more likely to focus on a problem or difficult situation. Not all scientists agree with them, however. Other studies argued that maybe, that cheerful music in the first experiment distracted kids from finding shapes. While scientists work on finding out the answers, it still might be wise to choose when to do your tasks according to your mood. After eating a delicious ice cream, for example, write an essay.
Answer: whether mood affects their learning ability
Example output: Researchers did experiments on kids in order to find out _ .
Example explanation: It is clearly mentioned in the article that to the check effect of mood on children is the main purpose of the experiment.
Q: Article: More and more people are taking their iPads to bed with them to surf the web, check facebook or send e-mails before switching off the light. But researchers are warning that the blue light their screens give off can stop users getting a good night's sleep. That is because this type of light is similar to daylight, convincing the brain that it is still daytime. Blue light prevents the production of a brain chemical called melatonin, which helps us fall asleep. By contrast, light which is more orange or red does not prevent melatonin production, perhaps because our brains recognize it as a cue that the day ends. Scientists have known for years that staring at screens late in the evening can affect sleep ---- they are television screens, computer screens or mobile phone screens. However, because mobiles and iPads are by nature portable ---- not to say addictive ---- more people are taking them into the bedroom. Users also tend to hold them much closer to their eyes than a computer or television screen. Researchers are warning that looking at iPad displays for more than two hours leads to lower natural melatonin levels as the devices give off blue light. They say, "Turning off the devices at night is the final solution. But if you have to use these devices at night, dim the display to cut down irritation of the eyes and limit the time you spend on them before bed." They wrote in the journal Applied Ergonomics that iPad makers should adjust the spectral power distribution of the devices so that they affect the sleep patterns of users less. It is not just a good night's sleep that could be harmed by too much late night screen time. Researchers know that long-term harm to sleep patterns can lead to an increased risk of obesity and even cancers.
Answer: it can help decrease the production of melatonin
A:
Blue light prevents iPad users from sleeping well because _ .