Which protein is responsible for unveiling the dna double helix 2 strands to prepare it for copying

The correct answer is DNA helicase.  

DNA helicases help in the unwinding of DNA. They play an essential function at the time of DNA replication as they distinct the double-stranded DNA into single strands, and permit each strand to undergo copying or duplication.  

It works by melting the hydrogen bonds, which holds the DNA into the double helical composition. The region of the DNA where the DNA helicase has unzipped the DNA is called replication fork.  

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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.