I just don't know what to do. I had little trouble getting through the first two questions but now I'm stuck on C and D is likely the same but for a base instead of an acid.

If the concentration of phosphate in the cytosol is 2.0 mm and the concentration of phosphate in the surrounding fluid is 0.1 mm, how could the cell increase the concentration of phosphate in the cytosol? a) passive transportb) diffusionc) active transportd) osmosise) facilitated diffusion