It only became runny because it was so hot outside.
Why the others are wrong:
A. it only became runny consequently it was so hot outside. "Consequently" means as a result, but in this context (the way it is being used), the sentence is essentially saying, "It only became runny and as a result, it was hot outside". That's not what the writer is trying to say.
C. Using "during" in this context is bad english and makes no sense. "It only became runny during it was so hot outside"
We can immediately eliminate C because he states that she was <em>unlike</em> the native people because she wanted a quiet life. We can also eliminate D because it doesn't fit the situation either. B also does not fit, as those subjects are never mentioned, leaving us with A.
