回复：24楼
老外可以根据需要，按规律随意造词，而且大家都能明白。比如一个名词后加less，可理解为缺少某物。至于beach person，cave person等，老外同样能够理解，并不代表必须词典里有才能用

同意，只要符合造词规律，或约定俗成就可以

be down
The reason I’ve been so down is all this work I have to do. 我之所以如此情绪低落是因为所有这些不得不做的工作
＝沮丧，情绪低落

be headed
Where are you headed next?
你接下来去哪里？
＝be going

in for
Now you’re in for a treat.
现在你要享受招待了
＝Guaranteed to get确定将得到

谢谢雾里山！

in the dark
I am as much in the dark as you are!
我跟你一样蒙在鼓里
=lacking knowledge 蒙在鼓里

Thank you very much for your contribution!
我在英语通里面的口语练习也学过这些内容！挺有用的！

回复：44楼
谢谢鼓励！

in the middle of things
Could I talk to you for a minute about the discrepancy I've found in this graph?
我能跟你谈会儿我在这张图上发现的差错吗？
—I'm kind of in the middle of things right now.
—我这会儿有点儿忙。
＝正忙着

on sale
I just saw an ad on television that said men's suits were on sale today and tomorrow.
我刚在电视上看到一则广告，说男士服装今明两天搞减价促销
＝大减价

on reserve
This table is on reserve.
这桌已预留给别人了
＝预留