Final answer:
The number of hours since sundown is directly proportional to the number of fireflies caught.
Step-by-step explanation:
The correct verbal description for the given proportional relationship is B) The number of hours since sundown is directly proportional to the number of fireflies caught.
In direct proportionality, as one variable increases, the other variable also increases proportionally. In this case, as the number of hours since sundown increases, the number of fireflies caught also increases.
For example, if it takes one hour since sundown to catch 10 fireflies, then after two hours since sundown, you would expect to catch 20 fireflies.