How do electrons become "excited"?

Which statement describes the appearance of a temperature-vs.-time graph? a horizontal line shows that the temperature increases at a constant rate over time. a vertical line shows that the temperature decreases at a constant rate over time. horizontal lines where the temperature is constant during phase changes connect upward-sloping lines where the temperature increases. horizontal lines where the temperature increases are connected by upward-sloping lines where the temperature is constant for each phase.

This is a characteristic of the elements in the periodic table that shows a pattern. it may increase or decrease across or down the table.

Mary is conducting an experiment on how pollution affects plant growth. how can she ensure that her data are reliable?