During the week ____ he tried tocollect materials for his article.

One learns alanguage by making mistakes and ______ them

Perhaps Taobao is Asia’s largest and most popular retail（零售的）network platform , _____ people can buy and sell a great variety of things .

We must do something to save wild animals.–You are right. We should make more rules to ___ wild animals_____being killed.

Einstein’s Theory of Relativity is so________ that most of us can not understand it.