In an Experiment on Way-Finding, Indigo Buntings Were Housed in Outdoor

In an experiment on way-finding, Indigo Buntings were housed in outdoor cages with blotting paper walls and inkpads on the floors. Which of the following facts demonstrated to researchers that the Indigo Bunting uses the positions of stars to orient its migration?

A) On clear nights, the footprint patterns were predicted.
B) In the spring, the inky footprints were mostly on the northern side of the cage.
C) In the fall, the inky footprints were mostly on the south side of the cage.
D) On cloudy nights, the footprint patterns were random.