Final answer:
Sexual dimorphism refers to the differences in physical characteristics between males and females of the same species. It is b) false that sexual dimorphism occurs when males and females are so similar that they are difficult to distinguish.
Step-by-step explanation:
Sexual dimorphism refers to the differences in physical characteristics other than reproductive organs that appear between males and females of the same species.
It occurs when males and females have distinct phenotypic differences, such as size, coloration, or adornments. For example, male birds often have more colorful plumage than females.
Therefore, the statement 'Sexual dimorphism occurs when males and females are so similar morphologically that they are difficult to distinguish' is false.