Which statement supports the author’s original statement that the beads found in south africa “have provided evidence that humans engaged in symbolic or modern thought over 75,000 years ago”?

a - before this discovery, many scientists believed that humans did not engage in symbolic or modern thought until 45,000 years ago.
b - there were forty-one beads that were discovered in blombos cave, south africa, that surprised many of the scientists.
c - these beads were made from the shells of small snails, which were similar to the shells found in other digs in south africa.
d - the beads were decorated and had human-made holes in them, indicating that people wore them, which is an example of symbolic thinking.