Good luck in your new job.中为什么要用luck?

Good luck in your new job.中为什么要用luck? I hope I can have a good luck in new year,have a new job may Good Luck in 2011, good luck with your new diet 是祝福语吗 good luck with your new diet and lifestyle Wish:New Year,good luck! good luck for your future? Good luck with your English good luck for your trip Your luck's so good Good luck （ ）your Japanese.A .to B.with C.at D.in 选哪一个?为什么? Good luck in your exam 的下句回答是?