呼吸运动实现了肺与外界环境的气体交换。平静呼吸的表达下面正确的是（  ）。

在探究“重力的大小跟什么因素有关系”的实验中，按照图甲所示，把钩码逐个挂在弹簧测力计上，分别测出它们受到的重力，并记录在表格中．

    I am Kate. I am a girl from New York.

    Today is Sunday. My1don't go to work, so they go to 2 their friends. I am3home alone. After I finish my homework, I'm4So I ask some of my friends to my 5and have fun.

    It's half past ten6the morning now. We are7diffrenet things. Look! Jack is playing computer8Someone may think it is 9 but Jack likes playing them. I am 10 some music on my MP3.11is Lisa doing now? Oh, she is 12to the music. She can dance very well. She 13to be a dancer when she grows up. As for Alice, she is14a newspaper on the sofa. We 15all having a good time.

新年联欢会上，共有90人参加了跳舞、合唱、演奏三种节目的演出．如果只参加跳舞的人数三倍于只参加合唱的人数；同时参加三种节目的人比只参加合唱的人少7人；只参加演奏的比同时参加演奏、跳舞但没有参加合唱的人多4人；50人没有参加演奏；10人同时参加了跳舞和合唱但没有参加演奏；40人参加了合唱；那么，同时参加了演奏、合唱但没有参加跳舞的有____ 人．