Sentence Correction

The explanation given for the correct answer is unclear to me. Please guide me.


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.