计算质量为10 千克的物体所受到的重力，下列各等式中正确的是（  ）

阅读短文，判断正误。

Dear Joe,

How are you? My sister and I are having our holiday. Yesterday we went to the library. We got there by bus. We read storybooks and had lunch there. The food was delicious. It was cheap, too. We went shopping in the afternoon. I bought a pair of shoes. I was very tired. We are planning to learn skating and do many other things during the holiday. We are sure we'll have a good time.

How about your holiday? Please write to me soon.

Miss you.

Alice

某历史学习小组围绕“西藏和平解放”“土地改革”“抗美援朝”进行研究性学习。该小组研究的主题应是（    ）

若代数式$\frac{\sqrt{2-x}}{1+x}$有意义，则x的取值范围是（　　）