For a forward bias pn-junction diode, diffusion capacitance

1. Linearly with current
2. Square of current
3. Inversely with current
4. Does not vary with current

For a forward bias pn-junction diode, diffusion capacitance is given by

C_D =	eI
	V_T

i.e. C_D I
Thus, we can say that for a forward bias pn-junction diode, diffusion capacitance varies linearly with forward current.