The 5vdc zener will keep point B at 5vdc no matter how high an applied voltage. The forward voltage drop of the conducting emitter/base junction will always be .7vdc.
I can not see the picture very well.
Think:
What voltage range can point (B) have? What does a zener diode do?.
What voltage range can point (C) have? What is a base like? What happens if you try to pull the base up? What happens if you try to pull the base down?
What voltage range can point (D) have? If transistor is on=0.7 If transistor is off then supply