I came across the following sentence correction question on an official GMAT practice exam - Can anyone explain why choice C is correct? It looks like the difference is the word them versus which.

Question:

In Hungary, as in much of Eastern Europe, an overwhelming proportion of women work, many of which are in middle management and light industry.

A/ as in much of Eastern Europe, an overwhelming proportion of women work, many of which are in
B/ as with much of Eastern Europe, an overwhelming proportion of women works, many in
C/ as in much of Eastern Europe, an overwhelming proportion of women work, many of them in
D/ like much of Eastern Europe, an overwhelming proportion of women works, andy many are
E/ like much of Eastern Europe, an overwhelming proportion of women work, many are in