--- Mum, I’m going to visit my aunt. What about a week? --- A week is too long. Try to be back in a ______ of days. 

Such men have made＿＿＿＿＿by developing oil businesses．

My English teacher is really very kind. I’ll never forget the ­­­______ he has done me.

It is the _______in the country to go out and pick flowers on the first day of spring.

Most air pollution is caused by the burning of ____ like coal, gas and oil.