求助OG12 SC6

Jackjokes

In late 1997, the chambers inside the pyramid of the Pharaoh Menkaure at Giza were closed to visitors for cleaning and repair because moisture exhaled by tourists had raised the humidity within them to such levels that salt from the stone was crystallizing.

这是正确的句子 我不知道怎么在论坛打下划线。。。 然后我想问D答案，为什么说D答案them有可能指代的是tourists？按照语法规则的话，根本就不是修饰的tourists啊。。
然后请求解释全题！ 谢谢