On Halloween, children in American like to _____ as ghosts to frighten people.
For many students, math is not something that comes _________. It takes effort.
The training program can give you a lift at work, ______ increase your incomeby 40%.
A recent research shows that there _____ volcanic activities on the moon and Mars. However, they no longer exist now.
If she had known what lay ____ for her, she would never have agreed to go.
The frozen waterfall has attracted floods of tourists to ____ the natural beauty.