观察以下课文原句并思考黑体部分的功能与构成。
1. These terraces were built by the local Zhuang and Yao people, to whom Guangxi is home.
2. Building the terraces therefore meant that they could increase the areas in which they could grow.
3. But perhaps what is most significant is the way in which people have worked in harmony with nature to make these terraces and grow rice.
4. This forms clouds from which rain falls down onto the mountain terraces once again.
