Extraversion is one of the Big Five, arrived at by factor-analysing thousands of trait descriptions. The concept itself came from Jung, whose method was clinical intuition. Why is that origin worth knowing rather than a historical footnote?

B. Because a construct can be proposed weakly and later vindicated.

The trajectory separates two things that get conflated: where a hypothesis comes from and what justifies it. Clinical observation is a fine way to generate ideas and a poor way to test them, and the factor analyses had no interest in Jung. The test could have failed, and for the rest of his typology it did, so we know which of his ideas was good, and why.