Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 38 to 42. Our eyes and ears might be called transformers because they send the light and sound around us and turn them into electrical impulses that the brain can interpret. These electrical impulses that have been transformed by the eyes and ears reach the brain and are turned into massages that we can interpret. For the eye, the process begins as the ...

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 38 to 42.

Our eyes and ears might be called transformers because they send the light and sound around us and turn them into electrical impulses that the brain can interpret. These electrical impulses that have been transformed by the eyes and ears reach the brain and are turned into massages that we can interpret. For the eye, the process begins as the eye admits light waves, bends them at the cornea and lens, and then focuses them on the retina. At the back of each eye, nerve fibers bundle together to form optic nerves, which join and then split into optic tracts. Some of the fibers cross so that part of the input from the right visual field goes into the left side of the brain, and vice versa. The process in the ear is carried out through sensory cells that are carried in fluid-filled canals and that are extremely sensitive to vibration. Sound that is transformed into electricity travels along nerve fibers in the auditory nerve. These fibers form a synapse with neurons that carry the massages to the auditory cortex on each side of the brain.

What does the word “them” in line 2 refers to?