The word that best fits the definition is "a. Acronym Abbreviation."
An acronym is a word formed from the initial letters of a series of words, while an abbreviation is a shortened form of a word. In the case of "NBA" representing the National Basketball Association, it is an acronym abbreviation because it is formed by taking the first letter of each word and combining them into a pronounceable word.
The other options, "b. Acronym Sentence" and "c. Basic Acronym," do not accurately describe the relationship between the given examples and their respective meanings.
In summary:
1. The word that best fits the definition is "a. Acronym Abbreviation."
2. An acronym is a word formed from the initial letters of a series of words, while an abbreviation is a shortened form of a word.
3. "NBA" is an example of an acronym abbreviation because it represents the National Basketball Association.
I hope this clarifies the concept for you. Let me know if there's anything else you would like to know.