Do you like to watch the advertisements on TV if _________?

Creating better health care, education and housing for everyone is a simple idea, but ____ which is hard to put into practice．

My family has two dogs. One is white, ________ is black.

一Which T—shirt do you like best?一     ．They are both out of fashion and expensive．

—Does your English teacher chat with you on QQ?—Yes, sometimes. It’s _______ we enjoy doing at weekends.