What Process Best Characterizes Ca²⁺ Movement from the Cytosol (Low

What process best characterizes Ca²⁺ movement from the cytosol (low Ca²⁺ concentration) into the endoplasmic reticulum (high Ca²⁺ concentration) ?

A) Calcium movement is spontaneous.
B) Calcium movement involves active transport.
C) Calcium movement occurs by facilitated diffusion using a transporter protein.
D) Calcium movement does not require energy.
E) Calcium movement occurs by passive diffusion.