Concept:The word "welfare" refers to the overall health, happiness, and general well-being of a person or group.
Explanation:In the given sentence, "the welfare of their students" means the state of students being safe, healthy, and comfortable.
We need to choose the option nearest in meaning to "welfare."
Option A, "wealth," means money or riches, which is not the same as welfare.
Option B, "happiness," is only one part of welfare, so it is too narrow in meaning.
Option C, "well-being," means the condition of being healthy, happy, and secure, which fully matches the meaning of welfare.
Option D, "growth," refers to development or increase in size, which is unrelated to welfare.
Therefore, the best substitute for "welfare" in the sentence is "well-being."
Answer:C. well-being