Read the passage from president barack obama's back-to-school remarks.

and that’s what i want to focus on today: the responsibility each of you has for your education. i want to start with the responsibility you have to yourself.

every single one of you has something you’re good at. every single one of you has something to offer. and you have a responsibility to yourself to discover what that is. that’s the opportunity an education can provide.

the repetition of responsibility in the passage obama achieve his purpose by

a. providing evidence to support his speech.
b. emphasizing the main idea of the speech.
c. showcasing his expertise at writing a speech.
d. soothing the audience with the rhythm of the speech.