The moment I completed the 800- meter race in the sports meeting, my legs _______.

If you want to know whether you are fit to learn history and geography, you’d better _________ your head teacher.

 Nowadays, no single country can successfully ____ the global problems alone.

 Jason has lost his job and is now _________ a very difficult time.

We can never expect _______bluer sky unless we create ______ less polluted world.