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Answer: ["A","D"]

Key insight
A step-stool is stable when the centre of gravity of the person + stool system falls within the base of support. Designs with legs angled outward or a wide base footprint are stable; designs where the top step overhangs unsupported structure will tip.

Step by step
Step 1: For each form, identify the footprint (contact area with the ground) and assess whether a person's weight on the top step falls within that footprint.
Step 2: Option A — legs splay outward from the base; the footprint is wide relative to the top step. Stable. ✓
Step 3: Option B — legs are vertical and directly under the top step but the geometry creates an unstable overhang condition when loaded at the top. ✗
Step 4: Option C — the frame leans or has an imbalanced structure that would tip when the top step is loaded. ✗
Step 5: Option D — legs splay outward in a stable scissor/X configuration; weight on top step stays within the footprint. ✓
Therefore the answer is A and D.

Why wrong options are wrong
Option B: The vertical-leg design means weight appli

Shown below are different forms for a step-stool. Which of the forms will remain stable when a person is standing on the top step?