His living conditions were difficult. However, he studied very well.

EASY answer

“His living conditions were difficult. However, he studied very well.”

⇒ He studied well despite his difficult living conditions.

A. wrong structure (excess “but”); C. wrong structure: Adj + as + S + be

B. doesn’t make sense (He does well in school thanks to living in difficult conditions.)

Structure: although + a clause ~ despite + N: although