Remember that identifying the conclusion is perhaps the most important step in answering logical reasoning questions. In this case it is kind of tricky, because the very first sentence is the conclusion. The rest of the passage is given as support for this first sentence.
Conclusion: "Ambiguity inspires interpretation."
Support: The ambiguous phrase "We are the measure of all things," has been interpreted in different ways. Basically, because the statement is unclear, different people understand it differently.
In this case, support for the conclusion is given in the form of an example. This is why D is correct.
E is incorrect, because the phrase "Ambiguity inspires interpretation" is not really a problem to be solved. Rather than being support for an argument, this statement IS the argument.
