1. the universe could grow indefinitely if a. dark matter reduces in size b. stars keep recreating themselves c. the universe is flat and full of matter d. the universe is flat and depleted of matter 2. when a low-mass star has used it's last remaining fuel, a occurs in which radiation ionizes the star's surrounding cloud a. nova b. supernova c. black hole d. planetary nebula 3. which terrestrial plane has an atmosphere similar to earth's? a. mars b. venus c. mercury d. none of the above 4. which is evidence that supports the big bang theory? a. the expansion of the universe b. the existence of dark matter c. the detection of dark energy d. the ow levels of hydrogen and helium 5. the most of the mass in the galaxy exists as a. galactic bulge b. dark matter c. exosolar planets d. stars

1. A
Recent study by NASA researchers had confirmed that the universe is made up of a great dark energy force called dark matter. The dark matter has been estimated to be about 95% of the mass of the earth. Scientists believe that, this dark matter will continue to push the universe to expand and that the earth will continue to expand indefinitely.
2. D
A planetary nebular is formed when a dying low mass star shed its outer layers completely. This result in a celestial object that is made up of glowing shells of ionized gases. Planetary nebular has a short life span compared to the life span of other astronomical objects.
3. B
The four planets that are closest to the sun are described as the terrestrial planets. The four planets are the Earth, Mars,Venus and Mercury. Out of these planet, the one that has a similar atmosphere to the earth's atmosphere is the VENUS. Both the Venus and the earth are composed of the same types of atmospheric gases.
4. A.
The big bang theory is presently the most widely accepted theory by scientists, which explains how the universe is formed. The evidence for big bang theory include: back ground radiation, the universe expansion and red shift. The evidence that the universe is expanding is obtained from the phenomenon of the red shift of light.
5.B.
The most of the mass in the galaxy exist as dark matter. Dark matter refers to the matters in the universe which do not emit any form of electromagnetic  radiation. They accounts for the gravity which hold the galaxies together and are made up of about 95% of the mass of the universe.