The portion of the Moon's surface that cannot be directly observed from Earth
A.
Sound absorption depends more on the thickness of a material than its color.
The best answer would be:
Unconditioned stimulus
In Pavlov's experiment on conditioning the food was the unconditioned stimulus that triggers a reflex or natural behavior. Think of it like something that makes you do something automatically.
For example, the food. When the dog smells food, it salivates. This is unconditioned because without teaching the dog, it automatically responds by salivating.
Eustress: m<span>oderate psychological stress interpreted as being beneficial for the experiencer.</span>
