What meiotic process, relative to the number of chromosomes of a given species, accounts for a significant amount of genetic variation in gametes?

The pachytene stage of the prophase I in the meiosis I division, the process of recombination occurs. The recombination is the process of exchange of gentic material of the same allele between the sister chromatids.

As the recombination result in the exchange of genetic material between sister chromatids, this result in the genetic variations in the progeny.

So, in meiosis 1 the recombination at the pachytene stage of prophase 1 causes a significant amount of genetic variation.

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.