Unit 9 · Speed and Time Calculation
Wildlife Hospital Staff — Ranking Levels
Lesson 2 of 9
A three-level structure holds food, water bowl, and a log. Two clues: food is below water, and food is below log. Which statement must be true? This is the simplest form of ranking deduction: when one item is lower than both others, it must be at the bottom — there is no other spot for it.
Three-item ranking questions with "must be true" phrasing are one of the most common OC TS question types. They test whether students understand the difference between "possible" and "necessary". Getting the right answer requires checking whether an arrangement is forced (must be true) or just one of several possibilities (could be true).
The examiner is testing whether students can deduce a forced position from two relative clues. Food is constrained to be lower than both other items — and in a three-level system, the only level lower than both remaining levels is the lowest. Options A and C are traps: the log and water can each be at middle or top, so neither is forced.
Three items must fill three distinct positions (e.g. levels, places in a race, floors of a building). Two clues each give a "higher/lower/before/after" relationship involving the same item. You must find which arrangement is forced — not just possible. The "must be true" phrasing is the key signal to look for forced, not optional, placements.
Best approach: List the constraints as inequalities: food < water, food < log. Ask: which position has the item lower than BOTH others? Only the bottom slot satisfies that. Then check the options: A (log = middle) and C (water = highest) are each possible but not forced — water and log can swap. D (food = middle) contradicts the constraints. Only B (food = bottom) is always true.
Question
Staff at a wildlife hospital are building a structure to house sugar gliders. The structure has three levels: one for food, one for a water bowl, and one for a hollow log that a sugar glider can use as a nest.
If the food is on a lower level than the water bowl and the log is higher than the food, which one of the following statements must be true?
Select an answer to see the explanation.
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