Question 1
Answer: E
Option B is false (although if you removed this because you have seen the film or read the book then consider yourself lucky! Remember, everything should be based on the text) because this is not an implication (indeed, the Rowling quote says that Snape made the "antiretroviral"). Option C and D are not assumptions, as C is explained in detail and D is presented as a possibility (no assumptions here, just a viewpoint). That leaves A and E. A is actually incorrect, Remus Lupin who we are told is a werewolf turns out to be a good character so they are not evil.
Option E, however, is an assumption because the author wrote "So, rather than seeing the apparently friendly Lupin as a friend, most adults will have read the story with impending doom in their mind as they suspect Lupin of acting with dishonest intent". The author here made the assumption that, because Lupin was a werewolf, readers would assume he was 'acting with dishonest intent'! Thus, the assumption is clearly that werewolves are perceived as evil.
Question 2
Answer: C
This question is cruel, there is no other word for it. Option A is the opposite of true in the main example given (about Remus Lupin) so is incorrect. Equally, there is nothing resembling the claim that adults would have realised that Dumbledore would die before the end. Equally, option E is presented as only something that "stargazers" may have realised and not the vast majority of adult readers. D is convincing but use of the word 'evil' is clearly too strong, the author says that "adults will immediately have spotted that Dolores Umbridge was, at least, not a very nice character". Hardly 'evil'! Our answer is C. "Duel-personality" is sufficient to mean "can turn into a different creature", you just need to give it the correct interpretation. In any event, it is possible to select C by process of elimination.
Question 3
Answer: D
This is the kind of Grand Logic question that you may even be able to work out before you read the options! Why not give that a go on the next similar style question?
Use of the phrase "main purpose" is important here. A and C are not anything close to a main purpose - they are incidental benefits of the text. The same goes for E because it is merely an interesting point made in the final paragraph about the link between HIV and Lupin's werewolf disease. We have to balance B and D. The reason that D is the correct answer is that the text is about Harry Potter (contrast that with the " Earthers" text used in the introduction lecture where "Flat Earthers" were actually not the main purpose for writing). Thus, we couple Harry Potter with the difference between children and adult reading abilities and we have D as correct and B as slightly less accurate.