The graph describes the motion of an object

the object moves with from a to b. it from b to c. it moves with from c to d.

first blank options- constant acceleration, constant velocity. or postive accelertaion
second blank- remains stationary, slows down, speeds up
third blank- same as blank 1

the object moves with constant velocity from A to B. It remains stationary from B to C. It moves with constant velocity from C to D.

Explanation:

This Position vs Time graph shows how the position changes with time and this is the definition of the velocity . This can be expressed as:

In the first segment AB, if we take two points and   the resultant velocity will be the same if we repeat the same calculation with any two points in this segment. This means the object  is moving at constant velocity.

In the segment BC, there is no change of the position in time, therefore the object is stationary during this segment.

Finally, in segment CD, the object has the same behavior as segment AB, hence it is moving with constant velocity again.

that tool is called an altimeter which measures your altitude which can be used to tell which atmosphere you are currently in, including the stratosphere.

hope this ! : )