Choice D is the best answer. This question tests dash usage for dramatic revelation.

1. Context clues: What follows dramatically reveals what "something extraordinary" is.
2. Meaning: A dash creates dramatic effect when revealing important information.
3. Verify: "The research revealed something extraordinary—a cure that worked in 95% of cases" creates effective suspense.

💡 Strategy: Use a dash for dramatic effect when revealing surprising information.

Choice A is incorrect because a comma doesn't provide dramatic emphasis. Choice B is incorrect because a semicolon requires independent clauses. Choice C is incorrect because while a colon works, a dash provides more drama.