2. what is the range of frequencies the human ear
can detect?

The human ear can respond to minute pressure variations in the air if they are in the audible frequency range, roughly 20 Hz - 20 kHz. It is capable of detecting pressure variations of less than one billionth of atmospheric pressure.

The linear perspective changed the quality of art because it gave art a sense of reality. it gave the illusion that the background and surroundings were actually close and/or far and a sense of depth. linear perspective change the quality of art following its birth the renaissance period as they want the art to be more realistic and they believe one way to achieve it is to use the method of linear perspective. it uses the principle of math to realistically portray space and depth in art. 

The theme of social protest remained a consistent focus for jacob lawrence throughout his career. in the 1960s lawrence was inspired by news reports and photographs, including images of segregated lunch counter sit-ins and stories of the   freedom riders in the civil rights movement. from the 1970s onward, lawrence's work focused less explicitly on contemporary social issues.