Which of the following is a sentence fragment in this excerpt from “No Dogs Bark”?

“I’m not doing all this for you. I’m doing it for your dead mother. Because you were her son. That’s why I’m doing it.”

(1 point)
Responses

“I’m not doing all this for you.”

"I'm doing it for your dead mother."

"Because you were her son."

"That's why I'm doing it."

None of the sentences in the excerpt are sentence fragments. All of them are complete sentences.

None of the sentences are sentence fragments in this excerpt from "No Dogs Bark".