Which of the Following Studies Would a Community Ecologist Undertake

Which of the following studies would a community ecologist undertake to learn about competitive interactions?

A) selectivity of nest sites among cavity-nesting songbirds
B) the grass species preferred by grazing pronghorn antelope and bison
C) nitrate and phosphate uptake by various hardwood forest tree species
D) stomach analysis of brown trout and brook trout in streams where they coexist
E) all of the above