Correct choice is (d) Unimportant
To explain: To make the voltage gain stable, a resistance rE is inserted in series with the emitter and therefore emitter is no longer ac grounded.
Because of this the ac emitter current flows through rE and produces an ac voltage at the emitter. If rE is much greater than r’e (emitter diode resistance) almost the entire ac input signal appears at the emitter, and the emitter is bootstrapped to the base for ac as well as for dc.
Thus the effects of the emitter diode become unimportant in swamping amplifier.