At the Isoelectric PH of a Tetrapeptide

Multiple Choice

At the isoelectric pH of a tetrapeptide:

A) only the amino and carboxyl termini contribute charge.
B) the amino and carboxyl termini are not charged.
C) the total net charge is zero.
D) there are four ionic charges.
E) two internal amino acids of the tetrapeptide cannot have ionizable R groups.