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 :)

Writing, you can revisit previous parts of the lesson by returning to the course map. be sure to refer to the lab’s student guide, which you can find on the first page of the lab experiment activity

The bags should be yellow i believe