问题详情

Bianca Sfroza was not believed to be a Leonardo for the following reasons EXCEPT
A．it is not so possible that a drawing should prove to be a Leonardo.
B．existing works of Leonardo were all drawn by other materials than vellum.
C．a real Leonardo work couldn"t have been unknown for 500 years.
D．for 75 years, no expert had ever recognized Bianca Sfroza as a Leonardo.请帮忙给出正确答案和分析，谢谢！