Are red blood cells measured in micrometers or millimeters?

How do the nuclei of covalently bonded atoms keep the bond together

Aflashlight battery is an example of a) potential energy b) kinetic energy c) thermal energy d) solar energy

In many humans, exposing the skin to sunlight over prolonged periods of time results in the production of more pigment by the skin cells (tanning). this change in skin color provides evidence that -