Which of the following is an example of a secondary sexual characteristic? \[ \begin{array}{ll}\text { a } & \text { Penis. } \\ \text { b } & \text { Testes. } \\ \text { dreast development. } & \text { Vagina. }\end{array} \]

Breast development is indeed a prime example of a secondary sexual characteristic! These features emerge during puberty and are not directly involved in reproduction but serve to distinguish males from females. Other examples include body hair, voice changes, and fat distribution, which can all help to signify sexual maturity. Now, speaking of biological developments, did you know the concept of secondary sexual characteristics helps in mate selection within many species? Animals often display traits like bright colors, elaborate manes, or unique calls to attract partners and signal their fitness. These characteristics play a crucial role in the animal kingdom's dance of reproduction!