Answer: D) pretentious.
Explanation: pretentious means something characterized by assumption of dignity or importance, especially when exaggerated or undeserved. Pretentious is the word that correctly fills in the blank, because its definition matches what it is being said about the man (that did not seem to have the experience that his boasting suggested). So the complete sentence would be: His actions were rather pretentious in that he did not seem to have the experience that his boasting suggested.