While researching a topic, a student has taken the following notes:
- Marine biologist Saira Okafor investigated whether healthy-reef sounds guide coral larvae toward settlement sites.
- Okafor released larvae into a chamber that divided into two arms.
- The arms had identical water flow, light, and substrate, and neither contained reef material or organisms.
- A speaker in one arm played a healthy-reef recording, while a speaker in the other arm remained silent.
- The playback and silent-speaker sides were switched in successive trials.
- Across the trials, 68 percent of the larvae entered the arm playing the recording.
The student wants to explain how the experiment’s design addressed both nonacoustic habitat features and a fixed directional preference as alternative explanations for the larvae’s movement. Which choice most effectively uses relevant information from the notes to accomplish this goal?