Which word in the following sentence is the antecedent of a pronoun?
ginger wanted to buy grapes, but the grocery store was out of them.
a. grapes
b. them
c. ginger
d. store

Okay, biology isn't exactly my strongest subject (it never has been), but i'm pretty sure the answer is nucleotides. dna is made up of nucleotides. each nucleotide contains a phosphate group, a sugar group, and a nitrogen base. there are four different nitrogen bases: adenine (a), thymine (t), guanine (g), and cytosine (c). a always pairs with t, and g always pairs with c.