Three word expressions are common in English. Practicing them and using them when you speak will help you sound more natural. Here are several common expressions, along with an explanation and example sentence.

black and white=something which is extremely clear(黑白分明的；绝对的)

       He told her in black and white that she couldn't leave the house while he was out.

　   dos and don'ts=the rules (行为准则，须知，注意事项)

       There are various dos and don'ts about driving in the UK.

haves and have nots=people who are rich and those who are not (富人和穷人)

       In London you can find the haves and have nots of the population.

ins and outs=the details (细节，始末，详情)

       I don't know the ins and outs of the situation, so I can't really advise you.

　　kiss and tell=when someone sells a story of themselves and a famous person (泄漏秘密)

       The British tabloids are famous for publishing kiss and tell stories.

odds and ends=small pieces of various items (零碎东西，零星杂物)

       She made a stew with the odds and ends she found in the fridge.

P's and Q's=manners (such as please and thank you) (言行)

       Mind your P's and Q's when you visit them!

pros and cons=advantages and disadvantages (赞成和反对)

      There are a few pros and cons that we should consider before buying a new house.

rights and wrongs=all the good points and bad points of a situation (事情的真相、全部)

      Regardless of the rights and wrongs of company policy, you need to give a month's notice.

tried and tested=something which has been well tested (经过反复考验的)

      Using salt is a tried and tested way of getting red wine out of a carpet.

ups and downs=good and bad periods following one another in turn(盛衰，沉浮)

      They have a lot of ups and downs in their relationship.

back and forth=not to stay still, but to keep traveling between two places (来回地，反复地)

       I'm so glad I'm moving. I was getting sick of going back and forth every day. Now my fourney to work will be a lot quicker.