Could you share a screenshot (or more) of the text and questions? If you go to the "review" tab you should be able to find the practice set.

Here are the screenshots and I have written a short paragraph about why I chose the answer I did for #8:

So I answered #7 correctly but did not provide the correct evidence.  I do not understand why these answer explanations for #8 seem to focus on the difficulty of studying/documenting collisions.  Since #7's answer was that collisions are COMMON, why would we be trying to prove that they're hard to document? Letter B for #8 was my answer choice because it shows that about half of the 126 studied galaxies showed signs of past or future collisions, therefore proving that collisions are fairly common. 

Thanks in advance for your help:)

Something certainly seems fishy with this question. What the system says is the correct answer doesn't seem to be related to supporting the claim that collisions are relatively common. Answer B certainly seems to be correct.

If you could submit a support ticket reporting the issue to our team, we can work on getting this fixed.

Thank you for posting! I was just as confused as you were when looking at the questions, so I'm glad you brought this to our attention. If you ever see anything else that looks off, definitely share it with us.

I just submitted a report on the actual page as well as through the link you sent.  Thanks!