Much to my astonishment, I found his lecture on wildlife conservation

A. Contrary to my expectations, his lecture on wildlife conservation was the most fascinating of all.

B. I was fascinated by what he said in his lecture on wildlife conservation though I hadn’t expected to be.

C. I hadn’t expected him to lecture on wildlife conservation, but he spoke well.

D. It was at his lecture on wildlife conservation that I realized I needed to study it.