Dear Poorvasha,

I'm happy to respond.

It's true that the "in that" structure is very sophisticated and formal, but all the language on the GMAT SC is sophisticated and formal, so this structure usually fits on the GMAT SC.

In this sentence, either "because" or "in that" would be correct. The problem in (A) is that the noun-modifying phrase that follows the underlined section is awkward--this phrase is meant to modify "tissue," not "tooth and bone," which it touches. The question of the phrase's target noun is ambiguous and muddy in (A), whereas (E) concisely cleans up this ambiguity.

Does all this make sense?
Mike
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My POE:
A) Was stuck between A and E and eliminated A because it sounds like "not normally found" is modifying BONE, but should be modifying tissues
B) LIKE is wrong, TISSUES are not LIKE TOOTH AND BONE
C) Same as B
D) COMPOSITION is being modified, but it should actually be tissues
E) CORRECT