Answer:
It is credible because Helen Keller is the author, writing about her own life.
Step-by-step explanation:
An autobiography is a book about a person's life written by that person. Here, Helen Keller describes her own feelings. She doesn't say anything unbelievable, anything that might get us to question the credibility of this excerpt. In fact, this excerpt is credible because Helen Keller wrote this about herself. If someone else claimed that Keller felt a certain way, we'd need to question that, because we need to ask ourselves: How can someone know how exactly someone else is feeling? This is why the second option is the correct one.