Look,Li Ming is [at] the computer括号中为什么用at请解析

You know __16__name is Li Ming.Look at the black car.It's my 阅读理解（英语）Look at the boy.His name is Li Ming.He is nine,too.M 急 急 急 根据句意,用括号中所给单词的适当形式填空 1 Li Ming is good at _ (talk) to Li Ming is ill,and now he is at the ___(doctor) Li Ming is good at swimming 的同义词Li Ming is____ _____ ______. is Li Ming at Tian'men Square 连词成句 we think that li ming is good at English Li ming is good at English.的同义句 boys and girs,_____(look)at the blackboard,please 请用括号中所给单词的 用所给词的适当形式填空 Li ming is good at ________(run) 英语翻译the frist student is Li Mling.piease look at the blackbo Look at the photograph.This is my family.为什么选at不选at或/