介词为什么不用in而是at?She was studying hard at the university.在大学里.不是in吗

介词为什么不用in而是at?She was studying hard at the university.在大学里.不是in吗 what are the rules at your school为什么用介词at不用in She is good( at )swimming,介词为什么用at? she works at a tvstation work为什么加S?本人初学者.还有 为什么用at 不用in on? She look after David at home.请翻译成汉语,为什么after.为什么不用at,for,或in. I’ll never forget the days___in which__ we worked together.为什么用介词in 不用at 有什么区别? 为什么要用at,而不用其他介词 She doesn't work hard at English,so she fails in the exam.为什么用fails不用failed? be poor in和be poor at这两个哪个对?she is poor at English.为什么用at不用in? occasion that 和 occasion whenoccasion 后面的介词为什么不用that 而是用 when? at school和in the school怎么区别,用法有何不同英语中诸如此类的介词用法怎么用?比如at the pinic为什么用at 而不用in.on my party为什么不能at my party? 介词in on at Mr.Johnson is the host the party is at his house.约翰逊先生是主人——聚会在他的家里举行.为什么用介词at?咋不用on呢?那为什么不用in啊？ does she have supper at six 为什么have不用has She is waiting (at) the airport为什么不用waiting for at that time 为什么要加介词at ,不是说,that后加时间状语,之前不用加介词吗? what do you usually do at weekends?at weekends为什么不用介词on noon在前面加的介词是at 那on a hot noon为什么不用at?