(D) says, "judgments about intrinsic value are always objective"
The problem with (D) is that we're concerned not with intrinsic value, but with extrinsic value. The entire argument deals with what it means if the value in question is not intrinsic. Thus, we can get rid of (D).
(C) says, "judgments about extrinsic value cannot be objective"
The argument in the stimulus makes the assumption that if the value is extrinsic, then it must be a matter of taste (that is, not objective). (C) captures the dubious leap of faith that the argument in the stimulus makes, so it's the correct answer choice.
Does this make sense? Let us know if you have any other questions!