The word "zealous" and "zeal" come from Latin roots that mean jealous. To be "zealous" is to be energetic with regard to something. It is a kind of "jealous anger" or "jealous energy"—not so much in the sense of being envious as in the sense of desiring something intensely. Thus, a zealous person is very devoted to his or her cause and could rightly be described as being "committed," which is the best option among those provided. 

The word "pensive" is related to the French "penser," as in the famous expression of Descartes: "Je pense donc je suis!"—"I think therefore I am!" Someone who is "pensive" is reflective and thoughtful. This does not mean that the person is necessarily deeply wise or intelligent (though this may quite well be the case). To be pensive means that you can ponder. Among the options, the best is "introspective." This means inward looking (=intro + spective). A person who is thoughtful, looks inward (so to speak) and reflects for a long time.

When someone is "diligent," he or she is devoted to his or her work. Now, while this would likely make you think that "devoted" would be the best option, actually "industrious" is slightly better. When someone is "industrious," he or she is works with great care and devotion. This expresses the role of work in the devotion better than the simple word "devoted." 

When someone is "thrifty," he or she is very careful with money. This does not necessarily mean that he or she is "cheap" or "stingy." Likewise, it does not mean that the person is "destitute" (poor). A wealthy person can be thrifty by buying things at a good price and not wasting his or her money. Now, "careful" may seem correct for this reason, but "economical" is better. When something is described as being "economical," it is an option that provides a good return for the amount of money spent on it. Therefore, this is the best option for a synonym for "thrifty."

"Zealous" is an adjective meaning having zeal or demonstrating energetic or fanatical support for a cause or person. "Fervent" shares the meaning of being fanatical. "Imprisoned" means held captive, "colossal" means huge, "lethargic" means tired and slow, and "apathetic" is an antonym of zealous meaning not caring at all.

"Gregarious" means sociable or enjoying the company of others, so "sociable" is the correct answer. None of the other answer choices are close in meaning to "gregarious": "innate" means natural or inherent; "disgusting" means causing revulsion or off-putting; "fertile" means productive, able to produce a lot of vegetation, or able to bear young; and "pungent" means having a powerful smell or taste.

Someone who is "elitist" is arrogant and thinks they are better than other people. The closer answer choice to this definition is "snobbish." To provide further help, "petrified" means very scared; "apprehensive" means cautious and worried; "desirable" means wanted; "nonplussed" means confused. 

"Distinguished" is an adjective used to describe a person who is accomplished, famous and eminent within their field. To provide further help, "permissive" means tolerant; "portly" means fat; "comely" means cute; "frivolous" means wasted, not necessary. 

"Formidable" means imposing and daunting. To provide further help, "reticent" means reserved; "timorous" means timid, easily frightened; "pusillanimous" means cowardly; "bestial" means savage, like a beast. 

"Unctuous" means excessively ingratiating, fawning, someone who debases themselves for someone else's approval. To provide further help, "abstruse" means hard to understand; "obtuse" means dim-witted, not smart; "acute" means sharp, quick-witted; "nominal" means insignificant.