It's used for v.ing.那请问为什么后面的动词要加ing呢？

It's used for v.ing.那请问为什么后面的动词要加ing呢？ what's for it used --What’s it used for?--It’s used for________.--What’s it used for?--It’s used for________.A.cook B.seen C.cooked D.to cook what's for it used连词成句 It's used for _____ _____ _____(探索太空） 尺子可以用来干什么用英语说what's it used for?It's used for _____(要回答）- -||| 英语翻译What's it used for?It's _____ _____ _____ metal What is it used for? It's used for testing for the p___ of the water It's fun 后跟 todo 还是v-ing 还是两个都可以 What's the machine used _____ It's used to ____ disabled people.What's the machine used _____ It's used to ____ disabled people.A.to,help B.for,help C.to,helping It's time for后面加动词原形还是动词ing形式? What is the Chinese for disher?It's used to dispense ice cream. it's used for type in information.type要怎么改吗吗 It's used for k____off rain,like an umbrella.请问画线处填什么 It‘s necessary that.(中文意思） get/be used to doing sth.(同上） be used for be used to do sth __what duo you call this in English?___It's a stamp .It's used _____sending letters.( 为什么这里要用FOR .不用TO.)sth be used to doing 也指被用来做=be used for 介词后加ING的问题介词后面的动词加ING还是介词后面（无其他干扰因素的情况下） 的动词加ING如for doing sth还是for sb.and one's sb.doingin a word就是介词后面加V的ING还是介词后面句子中的V加ING?