Consider the case of the car starting at rest and accelerating forward. A. Since the air inside the car is not leaking out, it must also accelerate forward. What object exerts the force that is responsible for accelerating the air forward? (I. e. the earth, the air outside the car, the car windows, the balloon, etc.)

The force originates from the tires. Tires accelerate the car. The car interior in turn accelerates the air inside the car by providing a pushing force. Thus it is the car read windows, seats and side windows that push the air forward causing it to accelerate.

Explanation:

The air inside the car is being forced forward by the car interior. This includes the rear windows, seats, side windows etc.

This accelerating force originates from the tires, and makes the car interior accelerate with the car. The air inside (since it has no direct connection to the tires) is then pushed forward by the windows, seats etc.

a and b sometimes have a positive value

scattering of light by tiny particles in air to produce the colors we see on sky, is dependent on the following factors:

(i) wavelength of light

(ii) size of the scattering particle  

(iii) distance traveled by light through the atmosphere.

according to rayleigh's law of scattering, the amount of scattering is inversely proportional to the fourth power of its wavelength. shorter the wavelength, greater is its scattering. hence violet/blue light is scattered more than red.

sun's light is a composite light ( visible light) with wavelengths in the range 400 nm (violet) to 700 nm (red). as sunlight passes through our atmosphere, the molecules of air scatter light according to their wavelengths. during sunrise and sunset, the sun's position is below the horizon. hence light from the sun travels a greater distance in the atmosphere when compared to its position a noon.

as sunlight enters the earth's atmosphere, blue light is scattered away and at the end of its journey in the sky, only red and orange wavelengths remain in the beam.

hence at sunrise and sunset, the sky appears reddish orange.