We arrived at the conference. Then we realized that our reports were still at home

Explanation: We went to the conference. Then we realized that our report was still at home.

A. As soon as we realized that our report was still at home, we went to the conference.

B. Only after arriving at the conference did we realize that our report was still at home.

C. Grammatical error (Not until + past clause / past landmark + inversion

D. Grammatical error (Hardly + had + S + V3/V-ed + when + S + V2/V-ed: as soon as…then)

→ Choose the answer NO