（单选题）Which of the following types of ion movement might be expected to require co-transport of protons from the mitochondrial intermembrane space to the matrix, inasmuch as it could not be driven by the membrane potential across the inner membrane? (Assume that each ion being moved is moving against its concentration gradient.)
选项：

A: import of acetate ions into the matrix from the intermembrane space
B: exchange of ATP from the matrix for ADP in the intermembrane space
C: exchange of Fe2+ in the matrix for Fe3+in the intermembrane space
D: import of Ca2+ into the matrix from the intermembrane space