20.When the hydrogen supply in the core begins to run out, and the star is no longer generating heat by nuclear fusion, the core becomes unstable and contracts. The outer shellof the star, which is still mostly hydrogen, starts to expand. At this phase the star is called a . a. White dwarf
b. Red dwarf
c. Red Giant
d. Black hole

Which of the following did you identify correctly

The correct answer should be "electrons orbit the nucleus in circular motions exactly as shown on the classic bohr model."

Is there any options, for this

1. why does the same side of the moon always face earthc.the rotational period of the moon is equal to one revolution around earth2. which is greater the moons period of rotation or its period of revolution  b.the moons revolution period around earth3.what was the major accomplishment of the apollo missions  c.sending the first human into space4. which of these space missions involved the deployment of lunar roversa. voyager 15. which scientists are going to explore next on kepler-186fd. evidence of existence of life6.which mission is not going to explore the outside of the solar  systemb.safir7.which technology limit the future of space explorationb. scientist must first develop certain technologies before missions can be completed.