Choice A is the best answer. This question tests dash usage for abrupt shift in thought.

1. Context clues: There's a dramatic shift between "on the verge of achieving" and "everything changed."
2. Meaning: A dash can signal an abrupt change or dramatic turn.
3. Verify: "The team was on the verge of achieving their goal—everything changed" effectively conveys the sudden shift.

💡 Strategy: Use a dash to signal an abrupt change in thought or a dramatic turn.

Choice B is incorrect because a comma doesn't convey the dramatic shift effectively. Choice C is incorrect because a semicolon suggests more measured connection. Choice D is incorrect because a colon typically introduces explanation, not abrupt change.