题目内容：

Limiting kids' recreational(消遣) screen time to less than two hours a day, along with enough sleep and physical activity, is associated with improved cognition(认知), according to a study published in The Lancet Child & Adolescent Health.

The study included about 4,500 US children aged 8 to 11 and measured their habits against the Canadian 24-Hour Movement Guidelines for Children and Youth. It found that 51% of the children got the recommended(建议) nine to eleven hours of uninterrupted sleep per night, 37% met the recreational screen time limit of two hours or less per day, while 18% met the physical activity recommendation of at least 60 minutes of accumulated physical activity a day. Only 5% of the children in the study met all three recommendations; 30% met none at all.

The researchers found that as each recommendation was met by a participant, there was a positive association with global cognition, which includes memory, attention, processing speed and language. Those who met all three had the most "superior" global cognition, followed by those meeting the sleep and screen time recommendation and finally the screen time recommendation alone, according to the study.

Other organizations, such as the American Academy of Pediatrics have guidelines in place to help with the management of children's screen time. The organization suggests putting realistic rules or limits in place for how long your children are on their screens, knowing who they are talking to and what they are doing. The amount of recommended screen time depends on the age of the child. Besides, parents should also make sure to encourage physical activity and have bedroom rules such as creating "tech-free zones".

1.Who are the target readers of this passage?

A. Researchers.    B. Teachers.

C. Parents.    D. Children.

2.What is the main idea of this passage?

A. A study on children’s screen time is published.

B. US children fail to meet movement guidelines.

C. Organizations are concerned about children’s cognition.

D. Limitation on children's screen time is linked to better cognition.

3.According to the passage, which of the following might contributes least to cognition?

A. Screen time limit.    B. Sleep hours.

C. Physical activity time.    D. Sleep hours and screen time limit.

4.Why does the American organization suggest creating "tech-free zones”?

A. To make sure children have enough physical playtime.

B. To make sure children have enough sleep time.

C. To make sure children have recreational time.

D. To protect children against radiation.