Which of the following statements about comets is true?
A.
Comets are mostly made up of rock. They are usually very hard to see, but as they approach the Sun the rock heats up and becomes much easier to see.
B.
Comets are mostly made up of rock. They are usually very easy to see but as they approach the Sun the rock condenses and becomes much harder to see.
C.
Comets are mostly made up of dust particles, frozen water and frozen gases. They are usually very easy to see but as they approach the Sun these particles condense and become much harder to see.
D.
Comets are mostly made up of dust particles, frozen water and frozen gases. They are usually very hard to see, but as they approach the Sun these particles heat up and become much easier to see.