OG-SC-26非常非常困惑

有一个OG语法题，困扰好久了，能帮忙解答一下吗？
26. Emily Dickinson's letters to Susan Huntington
Dickinson were written over a period beginning a few
years before Susan's marriage to Emily's brother and
ending shortly before Emily's death in 1886，outnumbering her letters to anyone else.

(A) Dickinson were written over a period beginning a
few years before Susan's marriage to Emily's
brother and ending shortly before Emily's death
in 1886, outnumbering
(B) Dickinson were written over a period that begins
a few years before Susan's marriage to Emily's
brother and ended shortly before Emily's death
in 1886, outnumber
(C) Dickinson, written over a period beginning a few
years before Susan's marriage to Emily's brother
and that ends shortly before Emily's death in
1886 and outnumbering
(D) Dickinson, which were written over a period
beginning a few years before Susan's marriage
to Emily's brother, ending shortly before Emily's
death in 1886, and outnumbering
(E) Dickinson, which were written over a period
beginning a few years before Susan's marriage
to Emily's brother and ending shortly before
Emily's death in 1886, outnumber

对于A 选项OG的解释我有点疑问，it is unclear what outnumbering refers to.
是因为26. Emily Dickinson's letters to Susan Huntington
Dickinson 离outnumbering太远？
还是因为outnumbering即可修饰主语，又可以修饰a period beginning a few years before Susan's marriage to Emily's brother and ending shortly before Emily's death in 1886？
还是因为被动语态就不能有伴随状语？