Is that your _______? 

Many countries are using natural gas , wind and other forms of ________ .

—Mum, I’m thirsty. Can I have some ______?—OK. Here you are.

 - Mr Li is said to be very patient with his students. - Yes. But it's really a hard_______ for him to control a class of young children.

Elephants like ________ but lions like ________.