This is an example of a prediction made by the theory of natural selection.

There must have been individuals in the population who were already resistant to the antibiotic. They would survive while the non-resistant bacteria would die out, leaving only the resistant individuals to pass on their genes by multiplication.

The bacteria themselves do not grow resistant to the antibiotic, and they cannot change their genetic makeup in response to the environment.

Since the drug is an antibiotic, not a sterilization method, it will not succeed in killing the entire population of bacteria.

This principle is particularly important in the field of immunology, as biologists work to figure out how antibiotic-resistant strains can be fought or maintained.

While natural selection is often described as "survival of the fittest," this explanation is not completely accurate. It paints the picture that the most fit individual lives the longest, when the real premise is that the individual with the most benefical combination of genes suited to the current environment reproduces more, thus passing on more genetic information to the next generation.

Bird wings and bat wings arose independently of one another, as they do not share a common ancestor with wings, therefore this is convergent evolution.

Divergent evolution implies a common ancestor from which different traits arise, so that is incorrect. It is not homology, as homology describes structures that are similar due to a common ancestry. Allopatric speciation is the emergence of new species due to a geographic barrier. Genetic drift is random variation in population genetic structure of a single species, which is unrelated to the topic at hand.

Allopatric speciation refers to the process by which a physical barrier separates a single population, causing two (or more) populations to arise and evolve due to environmental differences to become different species. Examples of factors that can lead to allopatric speciation include island formation, canyon and valley formation, and river paths.

Allopatric speciation occurs when a geographical barrier, like a river, mountain, or canyon, separates members of a population. This barrier prevents the individuals on one side from reproducing with the individuals on the other. In addition, selecting forces may act differently on the two sides of the barrier. This separation eventually results in two distinct species.

Here, the only example of allopatric speciation is that regarding the squirrels separated by the river. The example with the hawks refers to sympatric speciation, where no geographical barrier exists, but speciation can still occur due to other stressors. The remaining choices do not describe speciation at all.

Sympatric speciation implies a speciation event while the populations exist within the same geographical region.

Animals moving around more often does not really explain why speciation would occur differently, and plants are not necessarily less prone to chromosomal abnormalities. In fact, plants are more likely to be able to reproduce after abnormal chromosomal inheritance (nondisjunction, polyploidy, etc.) because many can self-fertilize. Instead of wandering around to find a mate, the plant can reproduce with itself and potentially create a reproductively isolated species.

Allopatric speciation results in the formation of a new species based on geographic separation of a population from its parent population. Geographic separation greatly restricts gene flow and, as a result of the isolation, other reproductive barriers may arise from the parent/ancestral species. Once reproductive barriers emerge in the allopatric population the ability to interbreed with the parent population may be prevented or highly impaired, even if the two populations were to come back into contact.

The other answer choices are factors of sympatric speciation, in which a population can give rise to a new species without geographic isolation.

Sympatric speciation refers to the evolution of a new species from a parent population without geographic isolation. The divergence into a new species requires the formation of a reproductive barrier that isolates a subset of the population from the rest, thereby blocking gene flow.

The formation of a reproductive barrier can result from polyploidy or natural selection. If a subset of a population chooses to only eat fruit that have fallen from trees while the rest climb the trees to eat, then the subset may eventually evolve different traits. Polyploidy creates a distinct genetic difference between individuals and can lead to difference phenotypes and reproductive barriers.

Allopatric speciation occurs when two groups of organisms are separated by a physical or geographic barrier. Common examples of these barriers include mountain ranges, oceans, and even large rivers. The isthmus of Panama is a prime example of a geographical barrier and it separates the Atlantic and Pacific oceans. 

Certain barriers are more easily traversed by some animals than others. For instance, an animal such as a cat is more likely to be corralled by a river than a horse or dog because the latter two are known to swim more often. But a river poses no threat of isolation to a bird. Because of their mode of locomotion birds are least likely to be hindered by a geographical barrier than a snake, raccoon, or even a prehistoric human (modern globalization almost entirely eliminates human's vulnerability to allopatric speciation).

Sympatric speciation occurs when a species of organisms becomes two different species whilst inhabiting the same area. Geographic barriers do not play a role in their divergence from one another. Allopatric speciation occurs because of a geographical barrier such as a mountain range. Sympathetic is not an evolutionary term and allosteric refers to specific sites on molecules in molecular biology and biochemistry.