निम्नलिखित में से किस प्रकार के रेत के टीले (बालुका स्तूप) सबसे दुर्लभ माने जाते 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?