In which of the following sentences does the pronoun come before the antecedent? a. the team played its best game of the season. b. the birds flew south to their winter home. c. his reputation was tom’s greatest possession. d. frieda enjoyed her collection of old books.

The sentence that the pronoun comes before the antecedent is: His reputation was Tom's greatest possession. The correct answer is option C. The pronoun used in the sentence is "His" and the antecedent referred by the pronoun "his" is the noun "Tom". 

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.