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?

Recent research ________ that trees belong to a type of social network.

In 2017, ecologist John Thomson and his research team discovered that forest trees communicate and share essential nutrients through a vast underground network. This remarkable ______ is made possible by fungal strands called mycelium, which connect the roots of various trees.3Mark for ReviewABCWhich choice completes the text with the most logical and precise word or phrase?AadjustmentBinterchangeCdemolitionDjuxtaposition

Explain the tree network topology'.

In graph theory, a tree is a graph that is:Connected with no cyclesDisconnected with cyclesConnected with cyclesDisconnected with no cycles

Text 1In separate studies, Joanna Weremijewicz and colleagues and Sanâa Wahbi and colleagues examined whether plants transfer nutrients to one another using a common mycorrhizal network (CMN)—a lattice of fungal strands in the soil. Weremijewicz and colleagues excluded all pathways other than the CMN by using barriers to keep the plants’ root systems separate while allowing mycorrhizal strands through—a crucial step Wahbi and colleagues’ study did not take.Text 2Weremijewicz and colleagues took the necessary precaution of separating the plants’ root systems (thereby excluding root-to-root transmission). However, any barrier used must allow the threadlikehyphae of a CMN to pass through, and this permeability would also allow liquids through. Thus, the researchers’ experimental design cannot ensure that any nutrient transfer observed can be attributed to a CMN and not to some other pathway.7 Mark For ReviewBased on the texts, the author of Text 1 and the author of Text 2 would most likely give the same answer to which question?A) Do plants that transfer nutrients through a root-to-root pathway also transmit nutrients via a CMN?B) Is there an available barrier material that can block roots and liquids while allowing fungal strands through?C) Are the barriers used in Weremijewicz and colleagues’ study sufficient to ensure that nutrient transfer could only occur via a CMN?D) Did Wahbi and colleagues’ study effectively exclude any nutrient pathway other than a CMN?