The correct answer is D. no article.
The word "able" is an adjective that describes a person's skills or abilities. It is not a countable noun, so it does not require an article.
The other options are incorrect because they are articles. Articles are used to introduce nouns. In this case, the noun is "man," which is a countable noun. Countable nouns can be singular or plural. When a countable noun is singular, it requires an article. The article that is used depends on the context.
In this case, the context is that the man is being described as being able. This means that he has skills or abilities. Skills and abilities are not things that can be counted, so the singular article "a" or "an" is not appropriate. The plural article "the" is also not appropriate because the man is not being identified as a specific man.
Therefore, the correct answer is no article.
