The correct answer is D. visible.
Vanity is often noticeable in a great leader because it can be a sign of confidence and self-assurance. However, it is important to note that vanity can also be a sign of insecurity and arrogance. Therefore, it is important for leaders to be aware of their own vanity and to manage it in a way that does not negatively impact their leadership.
Option A, desirable, is incorrect because vanity is not always desirable in a leader. In fact, it can be a sign of insecurity and arrogance.
Option B, admirable, is incorrect because vanity is not always admirable in a leader. In fact, it can be a sign of insecurity and arrogance.
Option C, remarkable, is incorrect because vanity is not always remarkable in a leader. In fact, it is quite common for leaders to be vain.
Therefore, the correct answer is D. visible.