More details so i can answer please
Lieutenant is not a part of the main clause, and it is an address to a person that is inserted into the sentence. It must be therefore separated by comas on both sides: the correct answer is a.
What are the sentences to choose from ?
I would feel slightly intimidated that somebody so young could be prepared for such jobs but starting earlier could help their experience. the expectations are high these days because apprenticeship is popular, but imagine how it was back then. It wouldn't completely put me off apprenticeship but I understand the uncertainty because of competition for employment and eagerness to impress/work hard under stressful conditions.
"Of" is a preposition in the phrase "Of studying" and "until" is another, as well as "to" in the phrase "to college" so there are 3 in that sentence.
