the correct idiomatic expression with 'differ' is 'differ in...', so a-b are out. (if you said 'differ because', you'd have to give the reason behind the genesis of the difference, not the nature of the difference itself.) that leaves c-d-e, which all contain the supposedly ambiguous pronoun - so you're stuck with it.
"being" is a big problem. if you don't realize it's a big problem, you should recalibrate your idea of what's a big problem and what's not.
remember, the gmat is the only authority on these things, and the gmat really, really, really doesn't like "being" when you're discussing the identity or properties of things.
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however, there's an even bigger problem: "because" is wrong.
in formal writing, "because" signifies an actual cause-effect relationship. if the latter thing didn't actually cause the former thing, then you can't use the word "because".
examples:
my brother and i are different in that he takes life much more seriously than i do.
according to this sentence, the way in which my brother and i are different is that he's a more serious guy than i am.
no cause and effect here.
my brother and i are different because he takes life much more seriously than i do.
according to this sentence, his more serious character, and my less serious one, have caused differences in us. in other words, the pre-existing difference in our character has actually led to further differences between us.
cause and effect relationship.
in this sentence, you're clearly trying to say that the cartilage rod attachment IS the difference, not that it causes the difference. therefore, "because" is incorrect.
As per Ron