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

A protruding tongue is indeed a characteristic physical feature often associated with Down syndrome. Individuals with this condition may have a tongue that appears bigger or may rest more forward in the mouth, leading to it protruding from the oral cavity. This can be attributed to various factors, including the presence of a smaller oral cavity and hypotonia (decreased muscle tone) which is common in individuals with Down syndrome. The characteristic features, including the protruding tongue, can contribute to challenges in feeding and speech development, making awareness and understanding of these traits important in providing appropriate support for individuals with Down syndrome.

The other options highlight features that may be present in individuals with other syndromes or conditions, but they do not specifically align with the distinctive traits commonly observed in those with Down syndrome. For instance, the downward slanting of the eyes is actually a more recognized feature, indicating that while there are various physical traits associated with Down syndrome, the protruding tongue is particularly notable for its frequency and impact on daily living activities.