how long“多长”,询问动作在时间上所持续的长度.其答语部分或划线部分可能是：

1）“for + 时间段”,有时可能没有介词for.如：

---How long did he wait for you here?他在这儿等了你多久?

--- For two hours. 两个小时.

It took him 20 minutes to finish his homework. (对话线部分提问)

→How long did it take him to finish his homework?

2）“since + 具体时间”,“since + 时间段 + ago”或者“since + 从句”.如：

---How long are you feeling like this? 像这样已经多久了?

---Since last night.从昨晚到现在.

3）表示时间的between…and…,from…to…等介词短语.如：

They were playing football from 9:00 to 10:00 yesterday. (对话线部分提问)

→How long were they playing football yesterday?

另外,how long也可以询问某事物的具体长度.如：

---How long is the desk?这张桌子有多长?

---1.2 meters. 1.2米.

how far“多远”,询问路程、距离.如：

How far is it from here to school? 从这儿到学校有多远

How far 的意思是多远,一般引导提问路程的特殊疑问句

例：How far is it from your home to school? 你家到学校有多远?

How long 的意思是多长时间,一般引导提问时间的特殊疑问句

例：How long have you been in America? 你在美国呆了多久?