The maths problem is ______ hard for us ______ solve.
Before you go to Canada, you need to learn more it.
Earthquakes always happen , so it is difficult to know when they come.
It’s every policeman’s dream to keep people and the traffic in good order.
We all find _________ important to do what the teachers tell us.
Don’t__________your dream. I’m sure your dream will come true one day.