1.be long for ; be long to do;什么意思

be long for 我没记错的话应该用主动的。。I long to see you 就是我很渴望见你的意思 也就是 很渴望（sth.）=look forward to +sth/doing sth.
leave sb. to do sth. 就是让某人去做某事。。
I left him to wash the windows. 就是我留他一个人去擦窗户。。
I left him there washing the windows就是我留他一个人在那里，他正在擦窗户。
leave sth done 就是留下某样东西处于一个完成的状态。如He left those windows cleaned. 就是他走了，剩下那些已经擦干净了的窗户。。

差不多就是这样的。。

【be long for sb/sth】【 be long to do sth】： to want sth very much especially if it does not seem likely to happen soon. (尤指对看似不会很快发生的事) 渴望。

例1： Lucy had always longed for a brother. 露西一直渴望有个弟弟。

例2： I'm longing to see you again. 我渴望再次见到你。

【look forward to sth/-ing】： to be thinking with pleasure about sth that is going to be happen (高兴地) (尤指对即将发生的事）盼望期待

例1： I'm looking forward to the weekend. 我盼着过周末呢。

例2： we're really looking forward to seeing you again.我们非常盼望能再见到你。

【leave sb/sth doing/to do/adj/undone】： to make