Domain represents all of the values that "x" can be.
In the illustration above, x represents time. Can time be negative? (No - unless you have a time machine!). So the smallest value that x can be is 0.
Now let's look at what happens when x is greater than 8....the y-value would be negative. In the illustration above, y represents depth. Can depth be negative? (No!) So the largest value that x can be is 8.
Answer: B. Real numbers from 0 to 8