What causes differences in air pressure

Air flowing from zones of high pressure to zones of low pressure causes winds, just like the way air gushes from a punctured tire or balloon. Uneven heating and convection generate the pressure differences; the same tendencies create currents in a saucepan of water heating on a stove.

Due to the difference of temperature

Air pressure is the force exerted onto a surface by the weight of the air. Some variations in air pressure are due to temperature differences caused by variations in solar energy received at the surface of the earth.Wind results from a horizontal difference in air pressure and since the sun heats different parts of the Earth differently, causing pressure differences, the Sun is the driving force for most winds.  

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.