The correct answer is allopatric speciation. Sympatric speciation occurs when two biological populations inhabit the same geography, but speciate due to behavorial differences. Parapatric speciation occurs when there is a small hybrid zone or overlap of two biogeographically distinct populations. Disruptive selection and natural selection do not explain events of speciation in the context of the question. 

The correct answer is sympatric speciation. Although rare, sympatric speciation occurs in populations that occupy the same geography, but still develop reproductive isolation. This isolation is generally driven by behavioral differences. Allopatric speciation occurs in biogeographically distinct populations. Parapatric speciation occurs when there is a small hybrid zone or overlap of two biogeographically distinct populations. Balancing selection refers to a mode of natural selection, not speciation. 

Mitochondrial DNA (mtDNA) is only inherited directly from a mother to her offspring and can be used to directly track lineage of a population or species. Nuclear DNA (nDNA) is inherited from both the father and mother of the offspring; it can be used to track lineage as well, but mtDNA similarity is enough to conclude a close relationship between the two populations described in the question.

Color, diet, and location are all distinguishing features of the populations and help characterize their niche in the ecosystem. Diet and location (territory) are not heritable traits, and do not signify ancestry. Color is genetic, but could result from convergent or divergent evolution. mtDNA similarity is the strongest available evidence for a close ancestral link between populations A and B.

In order to derive an accurate estimate of phylogenetic relationships, scientists need to use neutral DNA markers in their studies. If genes are under any sort of selection, it could completely change the results, because this may not reflect the actual evolutionary past of the organisms. It is also generally important to incorporate both nuclear and mitochondrial DNA, because these types of genes can show different histories (remember, mitochondrial DNA is inherited maternally).

Thylakoid membranes are found within chloroplasts, which are used for photosynthesis. Plants found in both aquatic and terrestrial environments photosynthesize, so these membranes cannot be considered adaptations uniquely benefiting terrestrial plants.

Comparatively, cutin is a waxy coating found on various parts of plants that helps prevent water loss when exposed to air. Stomata are tiny openings in the epidermis of plants that allow for the exchange of carbon dioxide and oxygen while minimizing water loss. Roots and root hairs allow plants to absorb nutrients and water from the soil. Water loss was the primary challenge plants faced when moving from aquatic to terrestrial environments; cutin, stomata, roots, and root hairs all help terrestrial plants absorb and conserve water.

Cell walls were present in plant cells before the transition to land. Seeds, stomata, waxy cuticles, and vascular transport all evolved to reduce water loss and circulate water to all areas of the plant. Water loss and circulation were not an issue before the transition to land; plants were forced to adapt these traits in order to survive in a terrestrial environment.

Swimming sperm is a feature of avascular and early vascular plants, who needed to remain in moist environments in order to retain water. 

After gaining vascular systems, plants were able to circulate water and nutrients more efficiently, thus being able to grow larger, have more leaves, develop branched systems of roots and shoots to collect water and nutrients, and better dispersal of spores due to gains in size. 

Plants developed more rigid structures to help maintain their growth on land as opposed to water.

Waxy cuticles developed to help reduce water loss/desiccation. Roots allowed plants greater access to water, as well as provided anchoring to the ground; this allowed plants to grow taller. Vascular tissue facilitated transport of water and nutrients to all parts of the plant. Stomata helped with gas exchange.

The occular, or eye piece, has a magnification power of 10x. If the 10x low-power objective were in place, the magnification would be multiplicative.

Optical transmission is the amount of light that passes through a laboratory specimen. It can be used to measure the concentration of components in the specimen. Optotype is the variable-sized type used in testing visual acuity. Visual acuity is a measure of the resolving power of the eye; the smallest type that can be seen at a distance. The index of refraction is defined as the speed of light in a vacuum divided by the speed of light in a medium. 

The resolving power of a light microscope is the smallest structure that can be seen, approximately 1 micrometer (a millionth of a meter) by the microscope.