During the horizontal line, the body was not increasing height, was vertically at rest.
Step-by-step explanation:
The graph given here is a graph between the elevation and time. This graph plots movement of a body on its y axis vs time where it's seen that the body is increasing steadily in height for the first 2 minutes from when it suddenly takes a horizontal line. It means that after 2 mins, the body comes to a rest at the vertical movement. For the next 3 mins, the body remained as the same state of movement, at vertical rest. After that, the body started coming down i.e decreasing its height for the next 2 mins. Then it again started increasing its height from reference ground, untill 9 mins after which it again came at vertical rest.