24) C

The text presents us with two possible explanations for the extinction of dinosaurs: space impact and super-volcanic activity. The text says that since it cannot be volcanic activity, space impact is the only plausible explanation. 
However, the text fails to recognise that there could be other explanations as well. So the assumption is that there are no other possible explanations for the extinction of the dinosaurs. 

A – Wrong
This statement just focuses on volcanic activity, which mean that this cannot be the answer. 

B – Wrong
Cooling of the atmosphere and acid rain is just an observation that would have been seen if volcanic activity had actually happened. It wouldn’t directly have made dinosaurs extinct. So this is not necessarily an assumption. 

C – Correct
This correctly identified the assumption that I discussed above. 

D – Wrong
This may seem like the answer. However, the scientists must take this statement as a fact and not as an assumption. 

E – Wrong
Changes in the ecosystems is not mentioned in the text so is irrelevant.  

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