The gradual variations in shape, color value, and shadowing in Siqueiros's Echo of a Scream refer to

The time characteristics of this selection?

a. ?are based on the tala cycle. b. ?are based on Western meter. c. ?feature an erratic pulse rate. d. ?feature a drum tala different from a voice tala.

Relative to art, one of man's important new cognitive developments was the ability to _________

A. use tools B. think symbolically C. write D. communicate verbally