关于独立主格，求大神们指点

Temporary-employment agencies benefit not only from the increasing demand for clerical workers but also the higher profits made when highly paid professionals are placed， requests for whom have increased in the recent wave of corporate takeovers.

　　（A） the higher profits made when highly paid professionals are placed， requests for whom

　　（B） the higher profits that are made in the placement of highly paid professionals， requests for whom

　　（C） from the requests for highly paid professionals， who make higher profits for the agencies when placed and whose requests

　　（D） from highly paid professionals， whose placement makes higher profits for the agencies and whose requests

　　（E） from the higher profits made in placing highly paid professionals， requests for whom

这题答案是E，楼主不明白逗号后面的分句做什么成分，是独立主格结构吗？如果是独立主格不应该是用现在分词或者过去分词修饰逻辑主语吗？可这里是have increased.

求大神解释！