In the markscheme they sketched the curve for the voltage out for the diode, the information given is that peak voltage for Vin is 3.4V and that the max voltage fo the diode is 0.7V. I understand why it would be half a cycle but I'm not sure about why the horizontal line is at 0.7V and why intially to begin with the diode already has a voltage of 0.7V and not 0V.