You are presented with the question "What do plants detect because of their circadian rhythm?" and the following answer choices: 
- Temperature changing
 - Life and death
 - heat produced
 - Soil and rocks
 - Light and dark
 - flow of electrons
 - Chemical energy
 - Rain and dryness

Now knowing that plants detect and respond to the daily cycle of light and darkness and circadian rhythms People and animals are usually adapted for a daily cycle of light and dark, choose the best answer.


 

     Light and dark    