You're pretty familiar with Earth already, but here are some facts just in case. Earth is the
third planet from the Sun, located in a "just right" distance so that it's neither too hot nor
too cold. Most of the planet is covered by water, and the air is a mixture of nitrogen, oxygen
and CO2. These are the two characteristics-water and the right mixture of gases-critical
for life as we know it. Earth is the only planet where we know life exists, although scientists
are pretty certain that some life form exists elsewhere in space. They just haven't discovered
it yet. Earth is hard and rocky, with meteor craters, mountains and valleys. It's also the fifth
largest planet.
ME
On which of the following space objects would scientists most likely expect to find life?
A
a planet with no solid surface
B
a planet with an ocean on its surface
с
a large planet very far away from the Sun
D
a small, rocky planet with no atmosphere