pronoun antecedent ambiguity

[shivani.magan]

In late 1990, the chambers inside the pyramid of the
virgin dreams 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 algae
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


Hi , in the question i understand that in option C and D ,"them" is ambiguous . It can refer to both the tourists or the chambers . But it is not clear why "them" in option E can refer to only the chambers and not the tourists? can some please explain this issue?

[tim]

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