Which answer best illustrates evolution by natural selection? a

 Best   the answer here is A. This is pretty much the definition for natural selection; a basic example is how Darwin theorised giraffes got their long necks. Over many generations, giraffes stretched to reach high branches = food. Only the taller giraffes reached the food, leading these to be the ones who would survive and hence breed, passing on their characteristic of a long neck. Fast forward many generations, and you have long necks in the entire species. 
Hope that helped a little :)

Ifound this on google “according to the findings, a foramen magnum positioned toward the base of the skull is found not only in humans, but in other habitually bipedal mammals as well.” i hope this you for what your looking for

The correct answer is d