GMAT Sentence Correction (SC) | Emily Dickinsons letters to Susan Huntington Dickinson were

SPLIT 1) PARALLELISM. ELIMY'S LETTERS OUTNUMBER HER LETTERS TO ANYONE ELSE. BLOCK OUT THE NOISE AFTER THE COMMA.
SPLIT2) Outnumber is a word that needs to be accounted. The clause inside called "which" is supplementing THEY. A clause needs to have a object and subject. Clauses do not have to be a complete thought. They need an object and a subject.

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