观察以下课文原句并思考黑体部分的功能。
1. These two pieces of information — the time of day and the point where the sun is in the sky — allow the butterfly to determine the way to go.
2. Eventually, it manages to reach the places where it will spend the winter.
3. The solution to the mystery of the monarch’s amazing ability comes at a time when it is in serious trouble.
4. Sadly, human activity is the main reason why the number of monarch butterflies is falling.
5. In many of the places where the butterfly can be found, people are destroying the natural environment.
6. If this works, there may come a time when the number of monarch butterflies increases once again.
