Mount Shasta is very impressive as per the author's view is option (A): Mount Shasta "is the single cone of an immense, extinct volcano."
Mount Shasta is an extinct volcano's cone that rises to nearly 14,162 feet above sea level, making it one of the biggest volcanic summits in the continental United States.
The main volcanic cone features a crater indent (a round hole at the top) formed during the previous glacial period. That is, it is a top in the shape of a cone.
The cones were formed by glaciers during the Ice Age, as well as volcanic eruptions.
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