C - Natural selection is causing larger bird beaks.
E - Because the seed hardness has increased the birds need bigger beaks to crack them.
R - This means the birds with larger beaks are not able to crack the seeds, this causes starvation and the birds that have small beaks die as a result. However, birds with larger beaks are able to crack the seeds and eat. Those birds can then reproduce and produce more birds with larger beaks. So the population of large bird beaks has increased, but the population of small bird beaks has decreased.
