Which of the following can be considered fossils?
a. a 1 billion year-old rock.
b. a 1 billion year-old piece of amber.
c. a 1 billion year-old piece of amber with a primitive insect inside.
d. all of the above

DNA contains the sugar deoxyribose, while RNA contains the sugar ribose. The only difference between ribose and deoxyribose is that ribose has one more -OH group than deoxyribose, which has -H attached to the second (2') carbon in the ring. DNA is a double-stranded molecule, while RNA is a single-stranded molecule