It usually takes rock "thousands to millions of years" before transforming into one rock type.
This is evident in the various research studies conducted, which show that rock transformation is so long that humans cannot witness its beginning or end process.
This is based on the research conducted by James Hutton in the 18th century.
The process of rock transformation is categorized into three which are crystallization, erosion and sedimentation, and metamorphism.
Hence, in this case, it is concluded that the correct answer is option D. "thousands to millions of years."
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