What do the experiments described in the tutorial suggest about internal clocks? They remain unchanged in the absence of external cues.
They require external light cues.
They have learned behaviors.
They have a genetic basis.

The sun produces a massive amount of energy due to the nuclear fusion reaction in its core, in which the element hydrogen is converted into helium. The temperature in the core is about 13,600,000 degrees Kelvin, and this heat is transferred into the next layer through thermal radiation.