Question

why do comets have tails?
a. earths gravity pulls the tail toward earth.
b. the sun vaporizes part of the ice of the comet.
c. comets are unstable and naturally disintegrate.
d. the suns gravity pulls them apart.

Explanation:

Comets are composed of ice, dust, and rock. When a comet gets close to the sun, the heat from the sun vaporizes part of the ice in the comet. The gas and dust released form a coma around the nucleus and are pushed away by the solar wind and radiation pressure, creating a tail. Earth's gravity has little to do with comet tails. Comets are not unstable in the sense of spontaneously disintegrating to form tails, and the sun's gravity is not what directly causes the tail - it's the vaporization and solar wind/radiation pressure.

Answer:

B. The sun vaporizes part of the ice of the comet.