Question

we often think of trees as simple objects that provide us with things we need, such as lumber, shade, or fruit. yet trees are far more complex—and social—than we recognize. an underground network of fungi, which some have called the \wood - wide web,\ connects the roots of numerous trees in a forest. using the network, trees can communicate with and support one another. they may share water, carbon, nutrients, and protective compounds with one another. scientists believe that one explanation for this phenomenon may be a \source - sink model.\ according to this theory, trees growing in excellent conditions with many resources transfer these resources to trees growing in less favorable conditions. in this way, trees in a forest ensure the health of the entire community by working cooperatively. what is the main, or central, idea of the passage? different parts of a forest may provide different conditions for trees, some more and some less favorable for growth. trees in a forest work to support one another by using an underground fungal network.

Explanation:

The passage starts by noting trees are more complex and social, then introduces the underground fungal network ("wood - wide web") that connects forest trees. It explains that through this network, trees communicate and support each other (sharing resources), and the "source - sink model" is a possible explanation. The first option focuses on forest conditions for trees, which is a minor point. The second option captures the main idea of trees using the fungal network to support one another.

Answer:

Trees in a forest work to support one another by using an underground fungal network.