这个句子如果按正常语序安排，应该是——
Many people / whosechances to do so were much inferior to Miss Martha's / have married.
可见 whose chances to do sowere much inferior to Miss Martha's 是定语从句，但是这种安排中的主语部分显然比两个词的谓语部分 have married 长得多，是一种外头重脚轻的臃肿结构，为了是句子平衡所以就把定语从句拖后，变成如下的结构：
主句：Many people havemarried 许多人已经结婚
定语从句：whose chances to doso were much inferior to Miss Martha's.
--[主语] whose chances to do so）这些已婚人结婚的机缘【不定式 to do so 是 chances 的后置定语，是 to get married 避免重复的代用形式】
-- [谓语部分] were much inferiorto Miss Martha's. 远不如玛莎小姐的（结婚的机缘）【Miss Martha's 是名词所有格，后面省略了前文出现过的 chance to do so】
