ANS:B - source resistor

JFET can be used as a Variable Controlled Resistor in the ohmic or voltage-controlled region i.e. for VDS < VP, whose resistance is controlled by the applied gate-to-Source voltage. As VGS becomes more and more -ve, the slope of each Curve becomes more and more horizontal, corresponding to an increasing resistance level.

The resistance value is given by rd = ro/(1- (VGS/VP))^2.

Hence, to get a -ve gate-source voltage in self biased JFET, we need source resistor. I hope, this is a bit clear.