Select the option which best fits the given blank/blanks. The teacher was…

In sentence-completion (vocabulary-in-context) questions, the missing word must match both the grammatical slot and the emotional/moral connotation set up by the rest of the sentence -- a word that is topically plausible but carries the opposite tone (positive instead of negative, or vice versa) will not fit, even if it is grammatically valid.

Here, the clause tells us the teacher was dismissed because of the act described in the blank -- dismissal is a serious, punitive consequence, so the missing adjective must carry a strong negative, morally-disapproving sense to justify it. "Unconscionable" means not guided by conscience -- unreasonable or unacceptable to a degree that violates basic moral standards -- which matches exactly the strongly negative tone the sentence's context demands for an act (helping students cheat) that led to dismissal.

Why the other options do not fit:

• "steadfast" describes firm, unwavering loyalty or resolve -- a positive quality that contradicts the negative consequence (dismissal) the sentence describes.

• "meritorious" describes something deserving praise or reward -- applying a praiseworthy sense to an act that caused a dismissal creates a direct contradiction with the sentence's tone.

• "pristine" describes something clean, pure, or unspoiled -- an unrelated, positive quality that carries none of the moral disapproval the context requires.

Because only "unconscionable" carries the strongly negative, condemnatory sense the sentence's context demands, it is the option that best completes the blank.