The correct answer is: Only I and II are implicit.
The statement “Dear students, if you want a healthy mind, listen to music” is a piece of advice. The Principal is advising the students to listen to music if they want a healthy mind. This implies that the Principal believes that listening to music is good for the mind. It also implies that the Principal believes that it is desirable to have a healthy mind. However, the statement does not imply that students normally like to follow good advice, or that it is the duty of the Principal to advise the students.
Here is a more detailed explanation of each assumption:
- Assumption I: Normally students like to follow good advice.
This assumption is not implicit in the statement. The statement does not say anything about whether or not students normally like to follow good advice. It is possible that some students do like to follow good advice, while others do not.
- Assumption II: It is desirable to develop a healthy mind.
This assumption is implicit in the statement. The statement says that if students want a healthy mind, they should listen to music. This implies that the Principal believes that it is desirable to have a healthy mind.
- Assumption III: It is the duty of the Principal to advise the students.
This assumption is not implicit in the statement. The statement does not say anything about whether or not it is the duty of the Principal to advise the students. It is possible that the Principal is advising the students because he or she believes it is their duty, but it is also possible that the Principal is advising the students because he or she cares about their well-being.