Read the following passage:
To test their theory, the researchers purchased a series of special lights that bathed the night-shift workers in a blue-green glow as they worked. When the shift ended the following morning, the workers wore special amber glasses to block out all blue and green light, thereby confusing their bodies into believing that they were working during the day and leaving at night.
Which of the following words supports the idea that this passage is fact-based? bought
special
ended
theory