Here "so" refers to "reported high satisfaction", therefore the parallel structure would be realized perfectly.
"More women reported high satisfaction" than" those who retired...".
同意楼上
首先排除which选项。如果用which,指代satisfaction则说的是satisfaction more。比较的对象是人数more。排除BE
再看平行比较结构。 women who took。。。。。more than those(women)who retired。。。。perfect。即可排除CD了
至于so 指代 reported high marital satisfaction。