①若实数a，b，c满足a+b+c=3，则a，b，c中至少有一个不小于1

②若z为复数，且|z|=1，则|z﹣i|的最大值等于2

③任意x∈（0，+∞），都有x＞sinx

④定积分 ${\displaystyle \int {}_0^{\sqrt{\pi }}}\sqrt{\pi -x^2}$ dx= $\frac{{\pi }^2}{4}$ ．

阅读下面文段回答问题。

        I'm Mrs Zhou. I'm a teacher in No. 1 Middle School(第一中学). This is Li Lei. He's Chinese. He is in Class 2, Grade 7. He's my student, and my son(儿子)too. He's twelve.

       That girl is Jean. She's American. She's eleven. And that boy is Jack. He's English. He's ten. They're in Li Lei's class.

I'm their Chinese teacher. All the students and the teachers have two names: an English name and a Chinese name. Li Lei's English name is Tom. My English name is Mary. Their English teacher Miss Jin's English name is Sue. Jean's and Jack's Chinese names are Wei Hua and Zhang Li.