Answer: B) maximum; minimum
Step-by-step explanation:
Pressure is the force exerted by a gas, a liquid or a solid on a surface (or area) .
On the other hand, density
is defined as the relation between the mass
and the volume
:

So, when the volume increases, the density decreases and when the volume decreases, the density increases.
Now, in the case of an automobile engine when the gas pressure builds up (increases) the volume of the expaned gas increases, as well. Since there is an inverse relation between density and volume, the density will decrease.