(4.05 lc)

the graph shows y as a function of x:

graph of x against y shows 4 segments. segment a is a horizontal line parallel to the x-axis. segment b is a slanting straight line going up. segment c is a horizontal line parallel to the x-axis. segment d is a slanting straight line going down that touches the x-axis.

in which segment is the function increasing?
a
b
c
d