He realized that the world could run out of key resources, ------------ he was a harsh critic of the wastefulness of modern industrial society.

A) so that
B) whether
C) so long as
D) and so
E) but

I have no objection to "D" but "A" could also be a logical answer . May I take your comments on the question please? And a last word, is double coordinative conjunction possible as in "and so"?

Thank you friends!