Other than bacteria, which factor leads to nitrogen fixation?
a. lightning b. flood c. rain

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A. Lightening

The energy produced by the natural lightening process breaks down the nitrogen molecules present in the air into atoms that combines with the oxygen present in the air results in the formation of nitrogen oxides. These nitrogen oxides combines with the rain water forming the nitrates. These nitrates gets deposited and absorbed by the soil. These nitrates makes the soil fertile.

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.