Why does the student mention that Barbizon paintings often had an unfinished appearance? A. To give an example of a feature she hopes to observe in Barbizon paintings at the museum. B. To give a reason why she is surprised that a major museum would host a Barbizon exhibit. C. To find out the professor's opinion about this aspect of Barbizon paintings. D. To point out that Barbizon painters often worked under difficult weather condition.