As opposed to primary sexual characteristics, changes in secondary sexual characteristics are most evident in changes in:

1. The secondary sexual traits start to emerge around puberty. 
2. Males and females look and act similarly until adolescence, with the exception of their fundamental sexual features. 
3. The development of facial hair, the enlargement of Adam's apple, the enlargement of the shoulders, the depth of the voice, etc. 
4. The expansion of pubic hair, softening of the voice, loss of upper body bulk, menstrual cycle, breast growth, and enlargement of the hip muscle are examples of secondary sexual characteristics in females. 
5. In addition to altering the body's fundamental sexual traits, they also affect how the body looks from the outside. 
6. Therefore, these traits cause a change in the body's outward appearance.

Hence, option D is the correct answer.