The experiment seemed to be proceeding perfectly _______ until the sudden power outage.

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Which choice completes the text so that it conforms to the conventions of Standard English?

A

perfectly,

B

perfectly;

C

perfectly:

D

perfectly—

Correct Answer: D

Choice D is the best answer. This question tests dash usage for abrupt shift.

  1. Context clues: There's a sudden interruption of the positive situation.
  2. Meaning: A dash signals an abrupt change or unexpected turn.
  3. Verify: "The experiment seemed to be proceeding perfectly—until the sudden power outage" conveys the abrupt shift.

💡 Strategy: Use a dash before an abrupt qualifier or unexpected interruption.

Choice A is incorrect because a comma doesn't convey the abruptness. Choice B is incorrect because a semicolon requires two independent clauses. Choice C is incorrect because a colon introduces explanation, not abrupt change.