A) complete the sentences.
as the cyclist rides along the road, the energy store in the cyclist's body decreases.
the speed of the cyclist is constant when the work done by the cyclist the work done against air resistance.

As the cyclist rides along the road, the _Chemical_ energy store in the cyclist's body decreases.

The speed of the cyclist is constant when the work done by the cyclist is__equal to__ the work done against air resistance.

Explanation:

When the cyclist start the bicycle, the chemical energy stored in his/her body as a result of food intake start consuming. This chemical energy is converted into kinetic energy when the cyclist exerts force on the paddle. This energy is then converted into motor energy or rotational kinetic energy which enable bicycle to move in forward direction.

The speed of the cyclist is constant, so there is no acceleration. According to the Newton's second law of motion, when there is no net force acting acting on any object, there is no acceleration. Acceleration is directly proportional to the net force applied on body.

                                F ∝  a

                                F = ma

 If a = 0, then

                                F = 0

Net work done is the product Net Force and displacement

                               W = F d

   If F = 0, then

                               W = 0

If the work done by the cyclist is equal to the work done against air resistance, then net work done is zero. So, speed of the cyclist is constant.