This important lesson by Professor Wang teaches primary students how to ______ themselves from danger.

The boy has poor eyesight because of _______ computer games.

__________ Tim’s help, I found my pet dog in the end. I should say thanks to him.[ ]

What does Mr. Liu usually ___________when he is at school?

Beijing ________ a lot over the years. Now it has become one of the biggest ______ in the world.