According to the biological species concept, for speciation to occur, according to the biological species concept, for speciation to occur, the number of chromosomes in the gene pool must change large numbers of genes that affect numerous phenotypic traits must change at least one gene, affecting at least one phenotypic trait, must change changes to centromere location or chromosome size must occur within the gene pool

The answer is; at least one gene, affecting at least one phenotypic trait, must change

This change, due to mutation, may result in an extreme trait in a small proportion of the population . If this extreme trait proves to be favorable with the environment it will continue to increase in the population with every generation. Eventually, the trait will become common in most individuals and the population will have speciated.

c. earths continental crust is thicker than its lithosphere.

because, the lithosphere is the outermost layer of the earth/ 100 km thick and is defined by its machanical properties.the lithosphere contains oceanic and continental crust that varies in age and thickness across locations and geologic time. the lithosphere is the coolest layer of the earth in terms of temperature. the term lithosphere should not be confused with the use of "geosphere" which is used to indicate all of earth systems, including the atmosphere, hydrosphere   and biosphere. the surface of the earth can be divided into the continental crust and the oceanic crust.   the continental crust is made mostly of granite while the oceanic crust is made of basalt. the average thickness of the continental crust is 25 miles and the average thickness of the oceanic crust is 5 miles.   three types of rock, igneous, sedimentary, and metamorphic, make up the surface of the earth. that's why 3 option is preferable.