Pronoun reference

[divineacclivity]

For the underlined portion of the sentence below, 4 choices are given to choose from in an example given in official guide for GMAT:<BR>In late 1997, the chambers inside the pyramid of the Pharaoh Menakaure 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 crystalizing and fungus was growing on the walls.

(a) Same as underlined
(b) Some other unclear and wrong phrase
(c) because tourists were exhaling moisture, which has raised the humidity within them to levels such that salt from the stone would crystalize
(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 crystalize
(e) because moisture exhaled by tourists has raised the humidity within them to such levels that salt from the stone was crystalizing

My query: The explanation given in the official guide for GMAT says that in choices (c) and (d), the pronoun “them” seems to be referring to “tourists” whereas in choice (e), the pronoun “them” correctly refers to chambers.

I’m not able to clearly see how “them” in (c) &amp; (d) choices refers to tourists but not in choice (e). Could someone please elaborate?

Thank you!

[srik07]

Among (c), (d) and (e), 'humidity within them' repeats ..so I would not prefer to split the choices based on that.

I would rather split it by parallel 'and' :'stone was crystalizing and fungus was growing' ..narrowing down to (e).

But surely the Official Guide explanation is confusing !!
Also I think the tense should ideally be 'had raised' rather than 'has raised the humidity', as the incident happened in the past and 'humidity had already caused the damage by the time chambers were closed' !!