OG12 SC 6中的指代问题

请教牛牛们：OG12-SC6的答案讲解中，说C和D中的them指代不清，指代的是tourists,那么为什么E中的them不会也让人误认为是指tourists？多谢！

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