地道美语：be up to = be doing sth 正在做sth

　　1.Let’ s rehearse, okay? "rehearse"”排练”
　　eg: We hadn’ t rehearsed often enough so I forgot my lines. 我们俩排练得不够所以我忘了台词．
　　The play rehearsal is on at 4pm today. 那个剧今天下午四点钟彩排．
　　2.As a symbol of my vow. "a vow "”n./v.发誓”
　　eg: He vowed never to cheat me again. 他发誓再也不会骗我．
　　Husbands and wives both take vows of sincerity. 丈夫和妻子要发誓忠于对方．
　　3.What are they up to? "be up to = be doing sth "”正在做sth”
　　eg: If my parents knew what I was up to they’ d be angry. 要是我爸妈知道我在干什么的话，他们会生气的．
　　A: What are you up to? 干嘛呢？
　　B: I’ m looking for my key. 我在找钥匙呢．