求助OG12-6代词指代问题！~

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.
(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
其他选项的指代问题我都明白~只有正确选项E里，我有些疑问them为什么不会有歧义指代离它更近的visitors呢？
求NN解答~先谢过的！~