Passage Summary: This specific plant has a root that is exactly half its height. More rain makes it grow taller, and high rainfall amounts always result in a plant that is taller than average.

Reasoning: The plant's taproot is always 50% of its height, and plants receiving more than double the average rainfall are always taller than the average height for the species.

Analysis: This is a 'Must be True' question, so we are looking for a mathematical deduction. We know two things: Root = 0.5 * Height, and High Rain -> Height > Average Height. Combining these, we can conclude that if a plant gets high rain, its root must be longer than half of the average height of the species. We are essentially looking for an answer choice that correctly manipulates these ratios and conditions without introducing any outside assumptions about the plant's biology.