Why do we need to use bacteria for gene cloning?

It is used in the step of transformation, in order to make more plasmid DNA and consequently more gene product of interest

Explanation:

DNA cloning, as a method in molecular biology, is used for the multiplication of gene (or other piece of DNA). It usually includes steps of DNA insertion into plasmid (prokaryotic circular piece of DNA). That plasmid is than introduced into bacteria via process called transformation. Transformed bacteria can produce large amount of a product of a certain gene, because of their fast gene expression.

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.