For these questions I often like to think of extreme answers to the questions and see if they change the evaluation of the argument. A) How many books had each person surveyed read? Doesn't matter because even if 1984 was the only book they had read it still could have the most influence on their lives (and indeed probably would) B) What if we said there were 1000 people surveyed and 990 of them chose books other than 1984? This would ruin the argument. We therefore need to know the answer to this question in order to evaluate the argument. C) Irrelevant D) Irrelevant because we aren't concerned with Orwell's other books, just 1984. E) Again, irrelevant, because we aren't concerned with whether they read it. We can all be influenced by books even if we haven't read them (like religious books, for example).
