Which of the following is a characteristic feature of Down syndrome?

Down syndrome, also known as Trisomy 21, is characterized by specific physical features and developmental traits. One prominent characteristic of individuals with Down syndrome is the shape of the head. A round head with a flat occiput is a well-known feature associated with this condition. This round face is often accompanied by other distinct features such as slanted eyes, a small nose, and a protruding tongue, which can further support the recognition of Down syndrome.

The other options represent characteristics that are either commonly seen in other conditions or are not specifically associated with Down syndrome. For example, a long neck with a prominent Adam's apple is often more typical of individuals without genetic abnormalities and does not pertain to Down syndrome. A cleft palate can be a feature of various genetic or environmental influences, but it is not a hallmark of Down syndrome specifically. Similarly, a highly arched palate is also not considered a characteristic feature of Down syndrome and may be seen in other conditions.

Understanding these characteristics is crucial for identifying and providing appropriate support to individuals with Down syndrome, as well as for educating others about the condition.