graph plotting help required

i wanna plot buck_boost converter's conversion ratio in matlab(.m) file.
i wrote this:

D=0:0.2:1;
x= -(D./(1-D));
plot(x,D)

now comes the questions:
1) i want x-axis on top with limits from 0 to 1 with step size 0.2 (changing from left to right on top). actually i want 'D' on x-axis . how can i do it ?

2) i want y-axis on left , starting from 0 and decreasing to -5 (0 -1 -2 -3 -4 -5 ) from top to bottom , how can i reverse y-axis ?

it would have been a lot easier if we were allowed to upload a picture . i hope to get my answers ASAP.

waiting badly