Researchers condition a flatworm to contract its body to a light by repeatedly pairing the light with electric shock. the stage in which the flatworm's contraction response to light is established and gradually strengthened is called:

acquisition

Explanation:

Flatworms are worms that appeared on Earth probably about 600 million years ago. They live mainly in aquatic environments such as oceans, rivers and lakes; They are also found in humid terrestrial environments. Some live free, others parasitize diverse animals, especially vertebrates.

These worms are extremely sensitive to certain light intensities, writhing quickly when an incident light causes electric shocks on their bodies. The moment that flatworms contort the body in the face of a light with gradually increased intensity is called acquisition.

i need

he forelimbs below belong to four species that descended in a direct line from the ancestral mammal shown above. of the four descendants shown, which species most likely appeared earliest in evolutionary history?