. . . . . . . . Sun sets in the West.

The correct answer is: C. the

The sun is a unique object in the sky, and it is the only object that we refer to with the definite article "the." This is because the sun is the only object in the sky that is always there. The other objects in the sky, such as the moon and the stars, are only visible at certain times of the day or night.

The definite article "the" is used to refer to specific or unique objects. In this case, the sun is a specific object because it is the only object in the sky that is always there.

The indefinite articles "a" and "an" are used to refer to general or non-specific objects. In this case, the sun is not a general or non-specific object because it is the only object in the sky that is always there.

The article "none of these" is not correct because it does not refer to any of the options.