Which of the following most logically completes the passage?

Each species of moth has an optimal body temperature for effective flight, and when air temperatures fall much below that temperature, the moths typically have to remain inactive on vegetation for extended periods, leaving them highly vulnerable to predators. In general, larger moths can fly faster than smaller ones and hence have a better chance of evading flying predators, but they also have higher optimal body temperatures, which explains why ______.

A. large moths are generally able to maneuver better in flight than smaller moths
B. large moths are proportionally much more common in warm climates than in cool climates
C. small moths are more likely than large moths to be effectively camouflaged while on vegetation
D. large moths typically have wings that are larger in proportion to their body size than smaller moths do
E. most predators of moths prey not only on several different species of moth but also on various species of other insects

I've couple of doubts in this question. Can someone help please.
- What is the conclusion?
- What kind of question is this? Main point, assumption, paradox, strengthen, weaken, etc?
- How the ans choice is solving the question?

[spoiler]OA: B[/spoiler]

Thanks in advance.