Why can a polymerase chain reaction be compared to a biological copy machine?

A polymerase chain reaction be compared to a biological copy machine Because, it is used to make millions of copies of a specific DNA molecule.

The method that is mostly used in the field of molecular biology is the PCR. This method is used for the purpose of making a specific DNA sample copies which can range form millions to billions. Thus, it helps a scientist to take only a smaller sample of DNA and then making it into larger amounts so that it helps them in studying their details.

There are some important steps involved in PCR. These includes, denaturation, annealing and extension of the DNA strands. As this method helps in creating large amount of copies of DNA it can be compared to a biological copy machine.

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.