We arrived at the airport. We realized our passports were still at home.

Mark the letter A, B, C, or D on your answer sheet to indicate the sentence that best combines each pair of sentences in the following questions

Question:

We arrived at the airport. We realized our passports were still at home.

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  A.
  It was until we arrived at the airport that we realized our passports were still at home.
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  B.
  We arrived at the airport and realized that our passports are still at home.
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  C.
  Not until had we arrived at the airport we realized our passports were still at home.
• 
  D.
  Not until we arrived at the airport did we realize that our passports were still at home.