Which Formula Allows You to Calculate the Membrane Time Constant $\tau$

Which formula allows you to calculate the membrane time constant $\tau$ _m?

A) $\tau$ _m = R_m/4 $\pi$ r²
B) $\tau$ _m = ir_input
C) $\tau$ _m = C_m V
D) $\tau$ _m = R_m C_m
E) $\tau$ _m = ΔV_max e^(-t/τ)