What does a vehicle's speedometer measure: instantaneous velocity or instantaneous speed?

The velocity-time graph of a body moving in a straight line is shown in the figure. The ratio of displacement to distance travelled by the body in time $t = 0$ to $t = 8 \ s$ is:

The figure shows a velocity-time graph of a particle moving along a straight line. The correct acceleration-time graph of the particle is shown as:

The figure shows the graph of the $x$-coordinate of a particle moving along the $x$-axis as a function of time. The average velocity during $t=0$ to $6 \,s$ and the instantaneous velocity at $t=3 \,s$ respectively,will be

What does $\dot x$ represent?

Which of the following curves does not represent motion in one dimension?