Question

cooperative trees
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.
the wood - wide web is an underground fungal network of connections between trees.
trees in a forest work to support one another by using an underground fungal network.

Explanation:

The passage first challenges the common view of trees as simple, then introduces the underground fungal "wood-wide web" network, explains that trees use this network to communicate, share resources, and support each other (with the source-sink model as a supporting theory), all to maintain the forest community's health. The first two options only cover single supporting details, while the third captures the core focus of trees cooperating via the fungal network.

Answer:

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