Answer
We can rank the points according to the gauge pressure:
$b \gt a = d \gt c$
Work Step by Step
Point b is inside the pipe with some water pressing down on it from above. Thus it has a higher pressure than point a.
Point a and point d do not have any water pressing down on them so the pressure at these two points is equal to atmospheric pressure; the gauge pressure is zero.
Point c is outside the pipe at a higher level than point d. Thus it is at a lower pressure than point d.
We can rank the points according to the gauge pressure:
$b \gt a = d \gt c$
