Which of the following is a well-defined set? Justify your answer. a. A collection of all boys in your class. b. A collection of efficient doctors in Black Lion Hospital.

To determine whether a set is well-defined, we need to assess whether the criteria for membership in the set are clear and unambiguous. a. **A collection of all boys in your class.** - This set is well-defined because the criteria for membership are clear: a student is included in the set if they are a boy and are part of your class. There is no ambiguity in determining who qualifies as a member of this set. b. **A collection of efficient doctors in Black Lion Hospital.** - This set is not well-defined because the term "efficient" is subjective and can vary from person to person. Different individuals may have different opinions on what constitutes an "efficient" doctor, leading to ambiguity in determining who belongs to this set. In summary, the collection of all boys in your class (a) is a well-defined set, while the collection of efficient doctors in Black Lion Hospital (b) is not well-defined due to the subjective nature of the term "efficient."