Christy wants to find out if the birds that visit the bird feeders in her backyard would
rather build nests in birdhouses or in trees. She puts a birdhouse next to the feeder
containing sunflower seeds and hangs a feeder containing cracked corn from a tree.
She observes the birds nesting activities over the next two weeks and records her
observations. Which of the following would improve Christy's investigation?
A. setting up a third bird feeder containing fruit near a bird bath
B. setting the feeders up closer to each other
C. putting the same kind of food in both feeders
D. putting more food in both bird feeders