The correct answer is D. no article.
The word “dollar” is a count noun, which means it can be used with a number and an article (a or an) to refer to a specific dollar. For example, “I have a dollar” or “I found an old dollar on the ground.” However, when it is used to refer to money in general, it is not used with an article. For example, “He can’t live on $100 a month” or “I need to make some money.”
The other options are incorrect because they are all articles. A and an are indefinite articles, which are used to refer to a general or unspecified thing. The is a definite article, which is used to refer to a specific thing. In this case, we are not referring to a specific dollar, so we do not need an article.