Final answer:
The correct answer is option B. Sima de los Huesos.
Step-by-step explanation:
The site known for yielding a sample of 4,000 fossil fragments representing about 28 premodern Homo sapiens individuals and comprising over 80% of all Middle Pleistocene hominin remains is B. Sima de los Huesos. This site is located in the Sierra de Atapuerca region in Spain. It showcases a significant collection of early human fossil remains, including those of Neanderthals and Homo heidelbergensis.
The diverse assemblage of fossils found at Sima de los Huesos provides valuable insights into early human evolution, anatomy, and the fairly large social groups they lived in during the Middle Pleistocene epoch.