1)是因为画家开始使用相机或者镜子这类视觉装置，画家照着反射在画布上的，自然画得很像realistic。

　　2)是因为开始使用油画，因为油画oil比别的材料的画干得慢，所以画家有很多时间去修正细节部分，让画看起来perspective。达到最佳角度。

　　Sample answer: In this lecture, the professor talks about two reasons why the paintings became more realistic and more perspective after Renaissance while the paintings before it seemed flat.

　　The first reason is that artists began using optical devices like camera and mirror to help them create their works. The professor points out that some artists would reflect an image in a mirror , trace the line on the mirror and then transfer their drawings to the canvas and subsequently paint over them. With this

　　method, they painted a bowl of fruits with the exact image reflected on the canvas, so the painting is more realistic.

　　The second reason is the use of oil paint, which dries more slowly than other paints. So it allows artists to spend more time on details. Before the paint gets dried, they could add second coats that are of different shades or colors, which then give their paintings depth, thereby adding perspective to the paintings.