GMAT Sentence Correction (SC) | Re: In late 1997, the chambers inside the pyramid of the Pharaoh

In late 1997, the chambers inside the pyramid of the Pharaoh Menkaure at Giza were closed to visitors for cleaning and repairdue to moisture exhaled by tourists, which raised its humidity to such levels so that salt from the stone was crystallizing and fungus was growing on the walls.

A. due to moisture exhaled by tourists, which raised its humidity to such levels so that salt from the stone was crystallizing
B.