Final answer:
Males in the ZZ/ZW sex determination system have two Z chromosomes, designated as ZZ. This contrasts with the mammalian XY system, and is observed in birds, some fish, crustaceans, insects, and reptiles.
Step-by-step explanation:
In organisms that use the ZZ/ZW sex determination system, males are characterized by having two Z chromosomes. Therefore, the correct answer to which sex chromosomes males have in the ZZ/ZW system is a. ZZ. This system is notably different from the mammalian XY system, where males are XY and females are XX.
In the ZZ/ZW system, it is the females that have distinct chromosomes (ZW), and the males that have a homogamous chromosome pair (ZZ). This type of sex determination is seen not just in birds (avian sex determination), but also in some fish, crustaceans, insects (such as butterflies and moths), and reptiles.
It's important to note the pioneering work of scientist Nettie Stevens, who was instrumental in discovering the role of chromosomes in sex determination. Although initially overlooked, her work laid the foundation for our understanding of genetic sex determination.