Sentence Correction

8. 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.
(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

OG 13 explain C D: them seems to refer to tourists
but E is correct
I think the C explain it that the tourists is close to them and the tourists is a subject. so them refer to tourists.
But I am confused that D and E the tourists is not a subject. and the D E have the similar structure. why the D's explain that them refer to tourists???

Pronoun ambiguity can be confusing at times. I have even heard that GMAC allows pronoun ambiguity if the sentence has some logical sense. I was not able to get a grip on that. It is better to look for other splits. Have Pronoun ambiguity as your last resort.

This sentence is about parallelism and 'due to' vs. 'because of'

Look here for expert explanation -> https://www.beatthegmat.com/pharaoh-at-giza-t52039.html

Elvin YY wrote:8. 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.
(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

OG 13 explain C D: them seems to refer to tourists
but E is correct
I think the C explain it that the tourists is close to them and the tourists is a subject. so them refer to tourists.
But I am confused that D and E the tourists is not a subject. and the D E have the similar structure. why the D's explain that them refer to tourists???

As gughan mentioned, pronoun ambiguity is tricky and should be used only as a last resort. There are OAs on the GMAT that have pronoun ambiguity, including this question. The 'them' in option E could refer to chambers as well as tourists.

There are better ways to answer this question. Ask yourself, why were the chambers closed?
Was it because 'tourists were exhaling moisture'?
No! So option C is incorrect.

Was it because of the 'moisture that was exhaled by tourists'?
Again, no. D is also incorrect.

The chambers were closed because the moisture (exhaled by...) had raised the humidity within the chambers to such levels that the salt was crystallizing. Option E has this right.

There are other issues in both these options. In C, 'levels such that' is unidiomatic - the right phrasing is 'such levels that'. Also, 'would crystallize' is not parallel to 'fungus was growing'.
In D also, 'crystallize' is not parallel to 'was growing'. And 'because of' is usually used before clauses, not nouns.