定语从句：
1.Then,things （you bought ）were wrapped in plain brown paper,or sometimes in old newspapers.
2.The bag--one of the simplest and most useful things in every man or woman's life--has given the world many strange expressions (that are not very simple)
过去分词做前置定语：
（Another widely used ）expression is "to let the cat out of the bag",meaning to reveal a well-kept secret.
倒装句：
When the dishonest tradesman opened the bag,out jumped a squealing cat ,not a pig.
本人自己做的,如有错误,请原谅