你说“应该是humidity",这个也不对哦,是 tourists -> moisture -> increased humidity to such levels that ... 整个这一串的逻辑关系
所以要解决问题,就是从源头切断——切断tourists这个环节,"were closed to visitors" 就像灭火一样,一方面切断燃烧源,另一方面消灭已经存在的火"cleaning and repairing" 像你说的"due to humidity" "caused by humidity",也没有抓住这题的逻辑。
due to=be caused by不等于on account of。是很直接的一种因果关系。本题中,cleaning and repair are caused by moisture是不对的,应该是humidity。
Th e sentence explains a causal sequence: visitors’ breath introduced moisture that caused salt to crystallize, which caused the chambers to be closed for cleaning and repair. Th e phrase due to makes this causal sequence somewhat ambiguous, seeming to suggest that the repairs were due to humidity from visitors’ breath.