What is the most essential characteristic of a statement for it to be considered a scientific hypothesis?

It must be a question about a natural event.

It must be supported by the scientist's personal opinion.

It must be a testable explanation for an observation.

It must be a well-established and proven scientific law.

A scientist hypothesizes that a population of deer is declining due to starvation. Which observation would most directly support this specific claim?

A survey showing an increase in the local wolf population.

Autopsies of dead deer revealing signs of malnutrition like low body fat.

Finding many deer tracks near a new highway built through the forest.

A decrease in the number of hunting permits issued for the area that year.

The darker soil at the pond's edge warms up and melts the nearby ice.

Ice melting is a very interesting phenomenon to watch during the spring thaw.

Why does the ice near the shore seem to disappear before the ice in the middle?

The overall air temperature is the single most important factor that determines when the entire pond will finally be free of ice.

The number of fishing boats operating in the area.

Water quality tests taken upstream and downstream from the factory.

A historical record of the fish population before the factory was built.

Lab studies on how the factory's chemical discharge affects the fish species.

Footage of cats frequently stalking near parrot nests.

Footage showing parrots and cats drinking from the same water source without interaction.

Footage of parrots successfully fighting off cats.

Footage showing parrots spending a long time searching for food but finding very little.