急!~请高手帮忙看看这道SAT语法IS题~THX

急!~请高手帮忙看看这道SAT语法IS题~THX
（One often coming upon passages in letters often that are ）memorable for their thought or their form, or both.
A. one often coming upon passages in letters often that are
B. one often comes upon passages in letters that are
C. one often comes upon a passage in letters that you find
D. often one comes upon a passage in letters; it is
E. often one comes upon a passage in letters in which it is
答案是B 但是我觉得B中那个that are指代不明（即,不知道是说passages还是letters）
我选的D 因为it只能指代a passage,而且IS中优先原则好像有断句优先于从句的说法?
5月7日就考试了,还请高手帮忙解释下~谢谢~