Question

The runners have just started a race. They started at rest and are getting faster.

Answer 1

A.  Acceleration is positive and speed is increasing.

Further explanation

The motion performed by a runner is part of a uniformly accelerated motion with constant acceleration.

Equation used  

$\tt \boxed{\bold{v_f=v_i+at}}$  

vf = final velocity  

vi = vo = initial velocity  

When a runner moves from rest, his speed will increase from being at rest (vi=0) and then move with a constant acceleration(a), and as soon as he crosses the finish line his acceleration will decrease (experience a deceleration ⇒a=- ) and decrease his speed until it finally stops

Velocity and speed are different because velocity itself is a vector quantity that takes into account direction and displacement, while speed is a scalar quantity (only distance).

So the speed does not take positive or negative values because it involves direction, while acceleration takes positive and negative values (deceleration) because it takes direction.