In terms of geographical size and population, South America can be described as:

South America is characterized by its vast land area, which is the fourth largest continent in the world. Despite this large geographic size, the continent has a relatively lower population density. This means that while there are significant urban centers and countries with considerable populations, the overall distribution of people across the continent is sparse due to various geographical factors such as the Andes mountains, the Amazon rainforest, and large stretches of uninhabited land. As a result, the combination of a large land area and lower overall population density accurately describes South America’s demographic and geographical profile.

In contrast, the other options don't reflect the continent's true characteristics. Some suggest higher population density without recognizing the vast uninhabited regions, while others describe it as small in size or medium, which doesn't capture the continent's extensive land area.