Answer:
The word "protracted" means lasting longer than expected, or unusually long, so what protracted most clearly means based on the context of the excerpt is how the time period of celestial motion studies must have lasted unusually long.
Answer:
Human uses of animals include both practical uses, such as the production of food and clothing, and symbolic uses, such as in art, literature, mythology, and religion. ... Animals serve as models in biological research, such as in genetics, and in drug testing.
