write on 写在...上的意思,写
例:Write on the form that you stayed so many nights at so much per night.
把你住了几个晚上、 每晚多少钱,填在这个表上.
write down 写下来
例:Write down the address before you forget it.
把地址写下来,省得忘了.
可以理解成write down(要写的内容)on (写在什么上)
个人建议可以不用具体记住两个词组,可以用对介词的理解来记住,down是一个向下意思的介词,而on是一个方位介词,表示在什么上面
不懂再问,