I'll preface by saying guessing, even educationally, is never a prime tactic...but i've been guilty of it too.
If I had absolutely no idea which answer was correct, I would choose the one that most supports the authors tone. If the author was strongly in favor or strongly against a topic, I would choose an answer that followed suit. Similarly, if the author was very mild/timid during the passage I would not choose an answer that makes strong, definite statements but rather one that again agrees with the authors tone.