In the 21st century, most Americans will marry three or four times ______.
Examples of the problems with the spread of specific invasive species in nature.
Now we could not do anything but (wait) __ for her here.
Most dieticians disagree with the concept of __ when dieting.
What happened more than 10,000 years ago?
A woman let fall ______.
Throughout the world 36 million people are suffering from AIDS, which is more than __ (整个澳大利亚的人口).