Today was my last day at work.
今天是我工作的最后一天.
I am busy with my work,so I can't have lunch with you.
我现在正忙于工作,所以无法和你一起吃午饭了.be busy doing sth和be busy for呢be busy for 后面跟表示一段时间的词，如：It won't be busy for long.它不会再忙很久了be busy doing sth 其实是：be busy in doing sth只是省略了in，如：The PC will be busy for several seconds (in) building a device list.PC将用几秒钟时间建立设备清单。（for也有了）