Answer: B: To expand the meaning of the word American to include all people.
In these lines, Kennedy addresses the question of civil rights, and in particular, the rights of black students to attend white institutions. He implies this in the sentence: "It ought to be possible, therefore, for American students of any color to attend any public institution they select..." The reason why he mentions the troops in his speech is because he wanted to make an analogy between the troops and the students. He argues that if black soldiers are considered American enough to fight abroad, then black students should be considered American enough to attend any college they desire.
