Choice B is the best answer. This question tests comma usage after introductory adverbs.

1. Context clues: "Reportedly" is an introductory adverb modifying the entire sentence.
2. Meaning: Use a comma after introductory adverbs like "reportedly," "unfortunately," "surprisingly."
3. Verify: "Reportedly, the new policy will take effect" correctly sets off the adverb.

💡 Strategy: Use a comma after introductory adverbs that modify the entire sentence.

Choice A is incorrect because it lacks the required comma. Choice C is incorrect because semicolons don't follow single-word introductory elements. Choice D is incorrect because colons don't follow introductory adverbs.