मध्य-महासागरीय कटक (Mid-ocean ridges) किस प्रकार की विवर्तनिक प्लेट सीमाओं पर बनते हैं?

The crescent-shaped sand dunes found in Sam, Jaisalmer are scientifically known as:

With reference to fjords, consider the following statements: I. They are deep, narrow inlets carved mainly by glaciers and later occupied by seawater. II. The shallow sill near their mouth is generally associated with glacial deposition rather than with tectonic uplift alone. III. They are chiefly associated with high-latitude or formerly glaciated coasts, rather than with humid tropical landscapes. How many of the statements given above are correct?