She could think of nothing more to say; but if he wished to converse with her, he might have better success. he stood by her, however, for some minutes, in silence; and, at last, on the young lady's whispering to elizabeth again, he walked away. why is jane austen’s sentence structure complex and refined?

If the options are:

A. Her sentences are simple, with only one clause each. 
B. Her sentences are unusual, with strange punctuation.
C. Her sentences are long, with more than one clause.
D. Her sentences use repetition for a sing-song effect.

I would say the correct answer is B. It's not just that these sentences are long and compound (composed of more independent clauses) - this fact in itself doesn't have to make them refined. They also exhibit the use of the semicolon, which is a very tricky punctuation mark. When used with care, it can speed up the pacing and even add more nuance to the meaning, which is exactly what Austen does.