Topic: Right Form of Verb,

Best Answer Explained in Below-:

The correct answer is "C) lest, should" due to the grammatical and contextual fit of the words in the sentence.

The sentence structure, "Build up your career — you ... repent," implies a cautionary message about the implications of not working towards one’s career goals. The word "lest" introduces a subjunctive clause that conveys the idea of preventing a negative outcome. It suggests that one should take action to avoid the regret that might arise from neglecting their career.

The word "should" is appropriately used in this context to express a recommendation or obligation. It indicates that an individual is expected to take proactive steps in their career to avoid future remorse.

Therefore, the phrase "you lest should repent" completes the thought, warning that if not careful in career-building, one may indeed regret their choices later on. The other options do not fit both grammatically and contextually, as they fail to create a coherent warning about the potential regret tied to career inaction. Thus, "C) lest, should" is the most logical and grammatically correct choice.