I still feel C should be the correct answer. B establishes the woody vegetation nests are less likely to be chosen by intruding Common Eiders, but does not give reason to believe wooden boxes are the preferred location to intrude (as apposed to the grasslands). However, if the word "established" is not conflated with the word "build" then C seems to be correct. The wooden boxes would not have "nest builders" and therefore be a better option than the woody vegetation and open grasslands that require nests to be built.

Thoughts?