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.

c. earths continental crust is thicker than its lithosphere.

because, the lithosphere is the outermost layer of the earth/ 100 km thick and is defined by its machanical properties.the lithosphere contains oceanic and continental crust that varies in age and thickness across locations and geologic time. the lithosphere is the coolest layer of the earth in terms of temperature. the term lithosphere should not be confused with the use of "geosphere" which is used to indicate all of earth systems, including the atmosphere, hydrosphere   and biosphere. the surface of the earth can be divided into the continental crust and the oceanic crust.   the continental crust is made mostly of granite while the oceanic crust is made of basalt. the average thickness of the continental crust is 25 miles and the average thickness of the oceanic crust is 5 miles.   three types of rock, igneous, sedimentary, and metamorphic, make up the surface of the earth. that's why 3 option is preferable.