Answer: stimulus
The students reaction is explained by the theory of classical conditioning first coined by Ivan Pavlov. The students are conditioned to associate the doer closing with the pop quiz and respond accordingly. Pavlov used dogs and their response to ringing a bell every time their food was served, after a some conditioning the dogs would salivate at the sound of the bell regardless of whether or not food was present. The bell was the stimulus.
Earth's earliest atmosphere lacks Oxygen, the gas necessary for life because it is a requirement for aerobic respiration.Oxygen does so many things for our body but It is the only respiration human body cells are capable of. Oxygen is needed for multiple reasons. It nourishes cells, allows the chemical transportation, helps toxins and waste material to break down and it supports and provides energy to our metabolism.
They had been hunting mammoths. They had followed them from Asia to North America.
