Choice D is the best answer. This question tests dash usage for parenthetical information.

1. Context clues: The phrase provides additional information about the policy's purpose.
2. Meaning: Dashes must be used in pairs for mid-sentence interruptions.
3. Verify: "The new policy—designed to improve workplace efficiency—has already shown..." correctly brackets.

💡 Strategy: Use matching dashes for parenthetical information you want to emphasize.

Choice A is incorrect because commas work but provide less emphasis. Choice B is incorrect because punctuation is needed. Choice C is incorrect because dashes must be paired.