When a red giant completes helium fusion and collapses, it becomes a
protostar
red dwarf
white dwarf
neutron star
black hole

Most short-period comets do not have randomly oriented orbits because

Which of these activities increases the amount of carbon in the atmosphere?

The illuminance of a surface varies inversely with the square of its distance from the light source. if the illuminance of a surface is 120 lumens per square meter when its distance from a certain light source is 6 meters, by how many meters should the distance of the surface from the source be increased to reduce its illuminance to 30 lumens per square meter?