请教og prep的代词指代问题。。解答自相矛盾

mogu724

In late 1997, the chambers inside the pyramid of the Pharaoh Menkaure at Giza were closed to visitors for cleaning and repair due 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. due to moisture that tourists had exhaled, thereby raising its humidity to such levels that salt from the stone would crystallize
C. because tourists were exhaling moisture, which had raised the humidity within them to levels such that salt from the stone would crystallize
D. because of moisture that was exhaled by tourists raising the humidity within them to levels so high as to make the salt from the stone crystallize
E. because moisture exhaled by tourists had raised the humidity within them to such levels that salt from the stone was crystallizing

答案是E
解析中说C的them指代tourist是错的，但是E中的tourist与C的是在同一个位置，就说人不会有humidity，不会有歧义，为什么呀？？、
请同胞们麻烦帮忙解答一下呢。。。。

mogu724

顶。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。求解答