In our class, when the bell rang and the teacher closed his book, it was a      for everyone to stand up. 

In my opinion, the most famous 　　　　 to tourists in the city is the wooden tower.

A new __________to teaching English, is being used here, and it has proven to be very helpful to the students. 

Global warming caused by human being’s casual behaviour has become a major _______ for people all over the world.

— There is growing _____ about house prices.— Don’t worry! Something has been done.