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, and many are E. like much of Eastern Europe, an overwhelming proportion of women work, many are in
"an overwhelming proportion of ..." is a quantity expression. most such expressions, although the words themselves are singular, take grammatically plural forms because they represent quantities that are clearly plural in number. for instance, percentages, proportions, fractions, and the like fall into this category. one-third of all the students are chinese --> correct. it'd be ridiculous to write "one-third of all the students is chinese". on the other hand. one out of three students is chinese --> also correct. in this case, you're literally saying one student (out of three), so, there you go, singular.
there are also other miscellaneous quantity words that are ostensibly singular but are used in the plural, such as "a dozen", "a trio", and so on. same deal.
in fact, "a lot" is probably the single most common quantity word in (somewhat less formal) writing, and that follows the same prescription: a lot of people were there. you would not, by any stretch of the imagination, write a lot of people was there.