Why does the conversation “seem like an eternity?”

In figure 4 of the telephone components what do the labels lettered a to e

Diego rivera was a famous artist from mexico. most of his paintings were murals. murals are paintings that are made directly on a wall. rivera thought that all people should be able to see beautiful art, not just people who could afford to go to museums. this is why he painted most of his murals on the walls of public buildings

Respond for free points because i don't have a question anymore.