Napping may be part of life for most of us.However，some countries where daytime naps have long been part of the culture，such as Spain，now discourage the habit.Meanwhile，some companies in the US now promote napping as a way to boost productivity. "It's important to try to reveal the biological pathways that contribute to the reason why we nap，" says Dashti from Harvard Medical School.
   Previously，co-senior author Richa Sexena at Massachusetts General Hospital（MGH） and he colleagues used many databases of genetic and lifestyle information to study other aspects of sleep.To gain a better understanding of the genetics of napping，they performed a genome（基因組）-wide association study （GWAS），which involves rapid scanning of complete sets of DNA of a large number of people.
   For this study，the researchers used data from the UK Biobank，which includes genetic information from 452，633 people.All the participants were asked to clássify their naps during the day as "never/rarely"，"sometimes" or "usually".The GWAS identified 123 regions in the human genome associated with daytime napping.Then the participants wore activity monitors called accelerometers，which can provide data about daytime napping.This data also showed that the self-reports about napping were accurate.
   Several other features of this study bolster its results.For example，the researchers obtained similar findings in an analysis of the genomes of 541，333 people collected by 23 andMe，a consumer genetic-testing company.Also，a significant number of the genes near or at regions identified by the GWAS are already known to play a role in sleep.
   The team also identified at least three potential mechanisms that promote napping.Some people need more shut-eye than others.A daytime nap can help make up for poor-quality sleep the night before.People who rise early may "catch up" on sleep with a nap. "This tells us that daytime napping is biologically driven and not just an environmental or behavioral choice，" says Dshti.Some of these mechanisms are linked to health concerns，such as a large waistline and increased blood pressure，though more research on those associations is needed.

（1）What did the researchers at MGH focus on in their new study？

C

C

A．The causes of long napping time.
B．The benefits of napping frequently.
C．The reasons behind the napping habit.
D．The genes contributing to poor sleeping quality.
（2）Why did the researchers use the activity monitors？

C

C

A．To study the database more efficiently.
B．To find the cause of genetic variation.
C．To guarantee the accuracy of the self-reports.
D．To explore how the participants feel after the naps.
（3）What does the underlined word "bolster" in Paragraph 4 probably mean？

B

B

A．Draw attention to.
B．Give support for.
C．Play a decisive role in.
D．Show different opinions on.
（4）According to Dashti，what will the researchers study next？

D

D

A．The ways to help people sleep better.
B．The causes of and solutions to some health concerns.
C．The impact of environment on people' s napping choice.
D．The connection between some health problems and the three mechanisms.