Passage Summary: Mushrooms can turn wood-based cellulose into a special type of branched glucose. When mammals ingest this, it doesn't kill cancer directly but instead kicks their immune systems into high gear to fight tumors.

Reasoning: Mammals cannot digest cellulose, but mushrooms can use it to create beta-glucans, which are branched glucose polymers. These extracts boost mammalian immune activity to fight tumors, with more branching leading to higher effectiveness.

Analysis: Since this is a 'Most Strongly Supported' question, we need to find a synthesis of the provided facts without overreaching. We know that the antitumor properties are linked to the 'branching' of the polymers and that these polymers are derived from cellulose. Therefore, the complexity of the molecular structure is directly related to how well the mammal's immune system responds. Look for an answer that connects the source (cellulose/mushrooms) to the specific immune-boosting result in mammals.