2:I[5751,[],""] 4:I[8003,["138","static/chunks/138-338b445c4cbceabf.js","3","static/chunks/3-b4862a6e1de95ec0.js","628","static/chunks/app/papers/%5BpaperId%5D/%5Byear%5D/%5Bid%5D/page-257c971832fd49dc.js"],"default"] 6:I[9275,[],""] a:I[1343,[],""] b:I[101,["138","static/chunks/138-338b445c4cbceabf.js","987","static/chunks/app/papers/%5BpaperId%5D/%5Byear%5D/layout-3942c697a7972a68.js"],"default"] c:I[6324,["138","static/chunks/138-338b445c4cbceabf.js","987","static/chunks/app/papers/%5BpaperId%5D/%5Byear%5D/layout-3942c697a7972a68.js"],"default"] 13:I[4080,["185","static/chunks/app/layout-f07fbac6855a712f.js"],""] 14:I[231,["138","static/chunks/138-338b445c4cbceabf.js","986","static/chunks/986-a23d2b0476d0b49a.js","368","static/chunks/app/papers/%5BpaperId%5D/page-879e8aaf99bd7bd0.js"],""] 16:I[6130,[],""] 5:T554,

Answer: ["A","D"]

Key insight
A chair rocks to and fro when its base forms a curved arc (rocker/runner) that allows it to tip forward and backward and return to equilibrium — a convex curved base in the plane of motion is the requirement.

Step by step
Step 1: Identify which chair designs have curved rocker bases (runners) in the front-back direction.
Step 2: Option A — has classic curved rocker runners at the base; will rock forward and backward. ✓
Step 3: Option B — has a flat or pedestal base that prevents rocking; may allow side lean but not to-and-fro rocking. ✗
Step 4: Option C — the base shape (X-frame or flat) does not permit the to-and-fro rocking motion. ✗
Step 5: Option D — has curved rockers in the front-back plane. ✓
Therefore the answer is A and D.

Why wrong options are wrong
Option B: The wide, stable pedestal base keeps the chair stationary and cannot rock.
Option C: The X-frame base contacts the floor at fixed points and cannot provide the rolling arc needed for rocking.

Remember for exam
To-and-fro rockin

Which of the chairs will rock TO AND FRO?