Why didn’t the Allied Powers, who knew the mass killings were taking place, focus their firepower on the ovens and the killing operations?

The Allied Powers didn’t focus their firepower on the ovens and the killing operations because at the initial height of the killing, they were incapable of doing anything militarily: Germany was winning the war in the Atlantic, and the Allied Powers, who were fighting to secure their own lands and lives, did not have enough soldiers and air power to fight in Europe. It was much later after a lot of killings, that the American Airforce was able to start bombing Eastern Europe in late 1943.

according to my calculation, the answer is d.