Fill in the blank (_) in the following sentence from the following choices.
Sentence: The puppies had weak eyes but sharp ears because the _ develop much faster in growing animals.

Choice 1: The puppies had weak eyes but sharp ears because the eyes develop much faster in growing animals.
Choice 2: The puppies had weak eyes but sharp ears because the ears develop much faster in growing animals.
Which of the choices is correct? Respond with only "1" or "2" and no additional text.
2
2. The puppies had weak eyes but sharp ears because the ears develop much faster in growing animals.