As far as we know all forms of life on Earth use ____________ as a medium for chemical reactions.
a. gaseous helium
b. gaseous helium
c. frozen carbon dioxide
d. liquid water
e. frozen water
Question 2
The habitable zone around a star is
a. the region on a planet where conditions are acceptable for life to exist.
b. a region around a star where a planet's temperature would permit the existence of liquid water.
c. very small for a massive star.
d. only found around G and K stars.
e. a region on a young planet where amino acids can begin to form DNA molecules.