gtest wrote:Teratomas are unusual forms of cancer <because they are composed of tissues such as tooth and bone> not normally found in the organ in which the tumor appears.

(A) because they are composed of tissues such as tooth and bone
(B) because they are composed of tissues like tooth and bone that are
(C) because they are composed of tissues, like tooth and bone, tissues
(D) in that their composition, tissues such as tooth and bone, is
(E) in that they are composed of tissues such as tooth and bone, tissues

I think the answer is A but E is the correct answer.

This is a hard one. If I saw this in a CAT I would just choose A and move on, but here are my thoughts:

The possible idioms are "X is unusual in that Y" or "X is unusual because Y." I'm not sure whether the latter is a correct idiom, but the former certainly is.

If you chose the first, then you could eliminate A, B and C. This leaves you with D, which is incorrect because composition is singular whereas Teratomas is plural, and E. So you'd be left with only E.

If you did not think of this first idiom immediately and tried to stick with the second one, you could have also worked off the fact that the sentence is a run on sentence:

"Teratomas are unusual forms of cancer <because they are composed of tissues such as tooth and bone> not normally found in the organ" in which the tumor appears.

You can fix it by changing the run on into a modifying phrase which C and E do by adding the comma after bone.

Hmmmm good explanation. Thanks

the question that helped me choose between A and E is
what is not normally found.
A says it's tooth and bone
E says it's tissues such as tooth and bone.