Answer:
B, air pressure in a car tire.
Explanation:
Discrete data is data which come in intervals, and isn't continuous.
The number of home runs can only go 0 -> 1 -> 2 -> 3, you can't have 2.5 or 3.2 home-runs.
The number of pills in a container can also only go 0 -> 1 -> 2. Again, can't have 0.7 pills.
The number of cars per household is also discrete. The number of cars in a household goes 0 -> 1 -> 2, you can't have half a car!
However, the air pressure is continuous. If you're increasing the air pressure, it'll (in theory) go from 0 -> 0.000...001 -> 0.000..002 etc. It doesn't "jump" from 0 pressure -> 1 pressure like the others, it goes smoothly. It can be any value.
So the air pressure isn't discrete data.