Remember the definition of acceleration:
a = Δv / Δt, this is change in velocity per unit of time.
Note that a and v are in bold to mean that they are vectors.
1) a body traveling in a straight line and increasing in speed: RIGHT:
Acceleration is the change in velocity, either magnitude or direction or both. So, a body increasing in speed is accelerated.
2) a body traveling in a straight line and decreasing in speed: RIGTH
A decrease in speed is a change in velocity, so it means acceleration.
3) a body traveling in a straight line at constant speed: WRONG.
That body is not changing either direction or speed so its motion is not accelerated but uniform.
4) a body standing still : WRONG.
That body is not changind either direction or speed.
5) a body traveling at a constant speed and changing direction: RIGHT.
The change in direction means that the body is accelerated. The acceleration due to change in direction is named centripetal acceleration.