The argument tells us that bumblebees are more efficient in pollinating cranberries than honeybees. That is because a bumblebee tends to visit a few species in a limited area, whereas a honeybee generally flies over a broader area visiting a variety of species. The only inference we can make from this fact is that the number of plants appears to correlate with the pollinating efficiency of a particular plant as (B) suggests.
(A) is too extreme as the stimulus only discusses certain crops, whereas (A) conclusion is about ANY of the species.
(C) contradicts the information in the passage that says bees visit a greater variety of species over a greater area.
(D) is an unwarranted inference, we cannot actually conclude that cranberries are typically found concentrated in limited areas just because bumblebees tend to pollinate in a limited area.
(E) is unsupported by the stimulus. We cannot conclude that there is a linear relationship between the likelihood of a given bee visiting cranberry plants and efficiency.