I am at school与I was at school的区别

I am at school与I was at school的区别 I am at school 还是 I am at a school at school in school 的区别?还有if i was you 和 if i were you的区别? I am a 什么 at willow school. i am at school(变为一般疑问句) I（be) at school I study at school .对否?I study in school 与有何区别? I am in No.5 Middle School与I am at No.5 Middle School这两种表达都正 I think I am popular at school.(改为一般过去时) I was at school at three yesterday afternoon.对at school 划线部分 when I was at school,I ( )a diary every day I am in school和I am at school有什么不同