Final answer:
Douglass gained the ability to educate himself by learning to read, which opened up a world of knowledge and allowed him to study different subjects and learn new things from books. So the correct answer is Option C.
Step-by-step explanation:
Fredrick Douglass gained the ability to educate himself through learning to read because it opened up a whole world of knowledge and information to him. By being able to read, he could study various subjects and learn about new things from books. This allowed him to expand his understanding and take control of his own education.