I was torn between two answers: E & B. E seemed correct because in the past, the passage Also, the passage stated "all Coelurosarus have been thought to possess feathers." This was a strong answer with a weak support in the passage.

The passage mentioned the fact the feathers were not present as an idea. This was a strong answer with weak support in the passage. I did not take this as proof or based on example of an Coelurosaur w/o feathers.

It seemed to me that feathers previously considered characteristic the point of debate around the discovery; a debate that was not closed on conclusion of the passage. Because of the use of the word "were" in the answers, it seems like answer suggested a belief before the recent discovery.

Any suggestions on how to pick between these two answers?

Ok. The reason to rule out E is that the passage states that "an entirely new - and apparently featherless - coelosaur has complicated the subject." They then theorize on why this is the case, but the fact is that this particular coelosaur lacked feathers, so "ALL" coelosaurs did NOT have feathers.
The answer choice in E doesn't suggest that at one point, we *thought* all coelosaurs had feathers, but rather states "feathers on dinosaurs were a characteristic of ALL coelosaurs." Since this is directly contradicted in the passage, based on the line above, it cannot be the answer.

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