how long,how much,how many有啥区别?他们的回答有何不同?

how long 多久,一般回答时间段如：How long have you been in this school?I have been here for about two hours。how much 多少,后跟不可数名词,回答用数量如：How much water is there in the bottle?There is little。How much 还有 多少钱的意思how many 多少,后跟可数名词复数,回答用数量如：How many students are there in your class?There are forty。