Which statement describes the mode of action of the ABCB1 transporter (the first eukaryotic ABC transporter to be recognized)?

A)During transport,the ligand binding site is alternately exposed to the exoplasmic and the cytoplasmic side of the membrane.
B)During transport,a conserved aspartate residue is phosphorylated.
C)This class of pumps transports only H⁺ ions.
D)This transporter acts as a chloride channel.