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


The pronoun - which can only logically refer to Emily Dickinson's letters as mentioned in the sentence. The subject of the sentence is Emily Dickinson's letters and not Emily Dickinson, for whom you will have to use the pronoun "who". 


Whenever you have a logical antecedent for the pronoun, do no be so rigid on the ambiguity rule. 


Only option E is correct. All the other options have other grammatical errors.  

- beginning, ending - function as modifiers that modify- "written over a period of time"

outnumbering is not a parallel modifier modifying written over a period of time.


Option B has a tense mismatch error and an error of parallel construction. 

Dickinson were written (past tense) over a period that begins (present tense)  a few years before Susan’s marriage to Emily’s brother and ended shortly before Emily’s death in 1886, outnumber her letters to anyone else.


“begins” and “ended” are not parallel


The sentence is 

Emily Dickinson's letters to Susan Dickinson which ( modifies letters).... written over a period of time.. (beginning and ending- modifier) outnumber her letters to anyone else. 

Option E correctly uses "outnumber" as a verb.