I don't want to use Mary's ball pen because I don't like( ).

I don't want to use Mary's ball pen because I don't like( ).
A) that ball pen of hers
D) that ball pen of her
答案选A,
选项A) that ball pen of hers= that ball pen of her pens
选项D) that ball pen of her中的her是宾格,做介词of的宾语,在此的her指人.没包含pen.