To achieve a speed of 6 m/s, the bottle must be dropped at m.

For an object dropped from rest, its speed after falling a height h satisfies v² = 2gh. Solving for height gives h = 6² ÷ (2 × 9.8) = 36 ÷ 19.6 ≈ 1.84 m. So the correct choice is 1.84 m.

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