Tricky answer choices to this one! I agree with theaether's analysis. But, let me do a full write-up for the record.
Let's breakdown the argument.
Conclusion: Legal responsibility is different than moral responsibility.
Premises: Moral Responsibility is based solely on intention. Legal responsibility sometimes depends on factors other than intention. For example, drunk driving + injury receives a stiffer penalty than drunk driving without injury.
We're asked to identify the role of the example. The example is of a situation in which something other than intention is used to determine legal responsibility. (D) nails it.
(A) is too extreme - the argument doesn't say that legal responsibility is based only on unintended features - there's no discussion of all the factors that go into legal responsibility. There might be some intended factors that go into legal responsibility.
(B) is tempting! The part in question is used to explore the criteria of legal responsibility, however the conclusion is not that the criteria that legal responsibility uses includes the factors that moral responsibility uses; the conclusion is that the factors are different.
(C) is incorrect because drunk drivers, causing injury or not, are legally responsible. The issue is that the severity of the penalty changes.
(E) is tempting! We do learn that moral responsibility depends solely on intentions, but the example we're looking at is not used to support that. In fact, that fact is a premise that is stated without support.
#officialexplanation