Natural selection takes place due to the differences or variation among individuals. Variation among species can help individuals to adapt to certain conditions. As a result, those organisms which are not able to adapt will eventually die, whereas organisms which can survive will be able to reproduce.

In this case, since there are two varieties of frogs–the fast-growing and the slow-growing, nature favored the slow-growing frogs. They are able to adapt to the conditions after the drought which decreased the population of their food source. As a result, they dominated the pond ecosystem over time.

B. natural selection

Choices A, B. C, and E are all incorrect. These ideas do not reflect the theory of Malthus about population growth. The correct answer is D. Darwin thought that the idea of Malthus was true. There are only a certain number of organisms that must survive to avoid overcrowding.

D. Organisms are able to produce many more offspring than will survive.

The surviving species has a high fitness. In biology, the term fitness represents an individual’s ability to adapt, live longer and reproduce more offspring in a given environment or condition. Therefore, the correct answer is C.

C. a better ability to survive and reproduce in the lake

The theory of evolution, which was proposed by Charles Darwin, explains how different species have evolved over time from their ancestors. Darwin discovered that the fossils of some animals that are already extinct have similarities to the living species.

B. changes in species over time

Homologous structures are shared by organisms that are related in terms of their evolutionary relationship. They usually have the same embryonic tissues during its development stage. However, when these tissues mature, their structures appear differently due to some modifications. An example of two animal structures that are homologous include the limbs of a mammal and the wings of birds.

C. homologous structures