I thought she was famous, but none of my friends have ______heard of her.      

—Are you going to Dalian by air?—No, the tickets are ____expensive for me. 

 Zhengnengliang, or positive energy, _______a term used in the book Positive Energy by Richard Wiseman, has developed into a popular phrase in Chinese society where people approach life with optimism and confidence.

 The computers in the other shop will be ______， but ______ as those in this shop.

The national parks are very important for the protection of these wild animals, which would ______ run the risk of becoming extinct.