哪位NN帮忙解决一下many of them 与many of whom 的区别-----大全987-379为例

379.      
In good
years, the patchwork of green fields that surround the San Joaquin
                    Valley
town bustles with farm workers, many of them in the area just for the
season.

(A)
surround the San Joaquin
                Valley town bustles with
farm workers, many of them

(B)
surrounds the San Joaquin
                Valley town bustles with
farm workers, many of whom are

(C)
surround the San Joaquin
                Valley town bustles with
farm workers, many of who are

(D)
surround the San Joaquin
                Valley town bustle with
farm workers, many of which（A）

(E)
surrounds the San Joaquin
                Valley town bustles with
farm workers, many are

答案是A，我觉得B选项如果不看前面的，也不考虑时态的话， many of whom are也对啊！

又看了看大全注释：

ffice:smarttags">ffice:smarttags">many of whom和many of them 的例句，还是不知道怎样区分！
    

many of whom例句：
                

I. In the United States
a significant proportion of the commercial honey supply comes from hobby beekeepers,
many of whom are likely to abandon
beekeeping with the influx of Africanized bees.

II. Voters in the city, many of whom
benefit from the low transit fares, are strongly opposed to increasing local taxes.

III. Saint-Simon’s followers,
many of whom were women, based their feminism on an interpretation of his
project to reorganize the globe by replacing brute force with the rule of
spiritual powers.

IV. The composition of this elite included vice-chancellors, many of whom
held office because of their wealth.

独立主格many of them

many of them通常修饰前面的词，如修饰主句则加with避免歧义。例如：

大全15. A new phenomenon visible at Managua’s major intersections is waves of vendors and beggars, many of them children, who mob cars at
the stoplights.

大全299. Florida will gain another
quarter-million jobs this year alone, many
of them in such high-paying fields as electronics and banking, making the
state’s economy far more diversified than it was
ten years ago.

大全498. The mountainous regions of northern Ethiopia are
dotted with hundreds of monasteries, many of them chiseled from solid
rock centuries ago.

哪位NN指点一下哈！先谢谢了！

B肯定不对，谓语动词的问题，我倒觉得c是可以的，不知道gmat是不是当先行词做宾格时，倾向于用whom