Four species of finch arrive on a newly formed galapagos island, which is covered with cacti growing in loose, dry sand. the cacti have honey-filled flowers and tiny seeds. the theory of evolution by natural selection would probably predict that would most succesfully survive, because
a) geospiza magnirostris; its large size makes it the fittest.
b) geospiza fortis; it will probably be able to dig up worms with its bill.
eliminate
c) certhidia oliveacea; its tiny pointed bill is the best adapted to sip nectar.
d) geospiza parvula; animals with intermediate traits tend to have higher survival rates in new places.

The answer is C) Certhidia oliveacea; its tiny pointed bill is the best adapted to sip nectar. 

In natural selection, genotype variations that will increase the chance of survival and reproduction of some organism are preserved and will be inherited. Among all mentioned species of finch, C. oliveacea has the trait that will best help it reach the flower under the sand. Neither the large size of birds, nor digging up worms, nor intermediate traits could help mentioned species (A , B and D choices) to survive if they cannot use the only available or the most common food resource, cacti. The only species with the greatest chance to survive is the one that is able to use available resources, and in this case, this is C. oliveacea because of its pointed bill for sipping nectar.