题目内容：

Getting kids to share their toys is a never-ending battle, and forcing them to do so never seems to help. New research suggests that allowing children to make a choice to sacrifice their own toys in order to share with someone else makes them share more in the future. The new findings are published in Psychological Science.

These experiments were conducted by psychological scientists, Nadia Chernyak and Tamar Kushnir of Cornell University. They found that sharing things with others when they are given a difficult choice leads children to think of themselves as people who like to share. It also makes them more likely to act in a pro-social （亲社会的）manner in the future.

Previous research has explained why rewarding children for sharing can backfire. Children come to think of themselves as people who don't like to share since they had to be rewarded for doing so. Because they don't view themselves as "sharers", they are less likely to share in the future.

Chernyak and Kushnir were interested in finding out whether freely chosen sacrifice might have the opposite effect on kids' willingness to share. To test this, the researchers introduced five-year-old children to Doggie, a sad puppet. Some of the children were given a difficult choice: Share a precious sticker（贴纸） with Doggie, or keep it for themselves. Other children were given an easy choice between sharing and putting the sticker away, while children in a third group were required by the researcher to share.

Later on, all the children were introduced to Ellie, another sad puppet. They were given the option of how many stickers to share (up to three). The kids who earlier made the difficult choice to help Doggie shared more stickers with Ellie. The children who were initially faced with an easy choice or who were required to give their sticker to Doggie, on the other hand, shared fewer stickers with Ellie. Therefore, children did not benefit from simply giving something up, but rather from willingly choosing to give something up of value.

“You might imagine that making difficult, costly choices is demanding for young children or even that once children share, they don’t feel the need to do so again,” Chernyak says. “But this wasn't the case: once children made a difficult decision to give up something for someone else, they were more generous, not less, later on.” Chernyak concludes.

1._______ helps children to share more in the future.

A. Rewarding children for sharing                      

B. Forcing children to share

C. Allowing children to share precious things willingly

D. Allowing children to share what they don’t need

2.The underlined word “backfire” means _______.

A. have an opposite effect                                              B. serve as a push

C. cause anger                                                                   D. avoid taking things back

3.Those who were required to share give fewer stickers to Ellie because _______.

A. they regret what they did                                           B. it’s not their own choice        

C. Ellie is not as sad as Doggie                                D. they like to share with a real person

4.We can conclude from the passage that _______.

A. parents will never find a way to get children to share toys

B. a gift should be given to make up for children’s sacrifice

C. children pretend to be generous when they are being observed

D. making difficult choices may influence sharing behavior