Final answer:
The word 'austere' best describes a teacher with a stern manner and a minimalist classroom approach, reflecting both strictness and simplicity.
Step-by-step explanation:
The word that best describes a teacher who is stern in manner and maintains a minimalist classroom is B) Austere. The term austere refers to someone who is strict or severe in manner or appearance, and often implies a stark or minimalistic approach. This word accurately captures the essence of a teacher who is not only stern in their demeanor, but also operates a classroom with minimal decoration or accessories, focusing instead on the essentials of teaching and learning.