At about pH 7 in most cells, what happens to the carboxyl R-group on an amino acid?

At about pH 7 in most cells, what happens to the carboxyl R-group on an amino acid?
A) It acts as a base and gains a proton, giving it a positive charge.
B) It acts as an acid and loses a proton, giving it a negative charge.
C) It is oxidized and tends to act as an electron acceptor in redox reactions.
D) It remains neutral, like water, and does not have a charge