Paragraph 7 suggests that Donald Grayson believes which of the following about the remains at Clovis sites and megafaunal extinctions? A. The rapid rate of the spread of humans explains why the extinctions also occurred at a rapid rate. B. The lack of evidence of human-caused extinctions is not surprising in view of the speed with which the extinctions occurred. C. It is likely that more evidence will be found as dating methods improve. D. If humans did contribute to the extinctions, much more evidence of that would have been found by now.