The appearance of fireflies at dusk is an example of a circadian rhythm because it

a. is related to the phase of the moon
b. is related to the temperature of the air
c. happens daily
d. happens seasonally

the right answer is C. happens daily

The circadian rhythm is studied by chronobiology. The circadian rhythm is the study of a 24-hour period during which a number of biological and physiological mechanisms are repeated. Circadian rhythms are modeled on an internal clock that regulates the rhythm of the waking / sleeping state, the rate of nail or hair growth, the rhythm of hormone production, blood pressure, the state of alertness, body temperature ... All living organisms have a circadian rhythm.

explanation:

on disadvantage of hydroelectric power is the cost. another disadvantage of using hydroelectric power is finding a water source powerful enough to harvest hydroelectric power.

a "theory" a suggestion that is not 100 % accurate, or a figure. some people say its a theory because they of all the passed theory's about one subject. it depends sometimes theory might be accurate and sometimes they are.