A couple is worried about having a child with a genetic disorder so they go to a genetic counselor. The counselor takes a sample of cells from their mouth to determine if there is a possibility of having a genetic disorder. Explain why they the sample from the mouth instead of simply looking at sperm or egg cells.

Besides finding pregnancy risks, genetic counseling can help you assess your own health risks. Test results can tell if you're at an increased risk for heart disease or certain cancers. For example, tests can find genes like BRCA1 and BRCA2, both of which are associated with breast and ovarian cancer.

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.