50.空腔理論的劑量計算可用  來表示，請問（？）可以是什麼？（  ：electron fluence）
(A)(S/ρ)total: mass stopping power
(B)(S/ρ)rad: mass radiative stopping power
(C)(S/ρ)col: mass collision stopping power
(D)(L/ρ)col,△: restricted mass collision stopping power