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

A. Not until we arrived at the airport did we realize that our passports were still at home.

B. We arrived at airport and realized that our passports are still at home.

C. It was until we arrived at the airport that we realize our passports were still at home.

D. Not until had we arrived at the airport we realized our passports were still at home.