若分式 $\frac{x^2}{x+1}$ 有意义，则x的取值范围是（   ）

     Joan is an American girl. She lives in China now. She is in my class. Her parents work in China, too, but her brother works in the U.S.A. He often writes letters to them. Joan likes Chinese class very much, and likes speaking Chinese with us after class. Her father teaches us English well. We all like his class. On Sundays, Joan goes to the People's Park with her father and mother. Sometimes she goes shopping with her mother. They like the Chinese food very much. It's a happy family.

如图是模拟呼吸时膈肌的运动情况，请根据图回答问题  

已知集合 ，则（    ）

空气中含量最多，且可以做保护气的气体是（   ）