The correct answer is: C. One of
The sentence is “One of the girls was selected for national scholarship.” This means that only one girl was selected, not all of them, not some of them, and not many of them.
The answer “Some of” is incorrect because it implies that more than one girl was selected. The answer “All of” is incorrect because it implies that all of the girls were selected. The answer “Many of” is incorrect because it implies that more than one girl was selected, but not all of them.