The correct answer is C: is. This question tests subject-verb agreement with nouns that appear plural in form but are singular in meaning. "Economics" is an example of such a noun. Many academic disciplines, fields of study, or diseases ending in "-ics" are treated as singular subjects, even though they end with an 's'. Other examples include "mathematics," "physics," "politics," "statistics" (when referring to the field), "news," and "mumps."
When "economics" refers to the academic subject or the overall study of production, distribution, and consumption of goods and services, it functions as a singular noun. Therefore, it requires a singular verb. "Is" is the singular form of the verb "to be" in the present tense, correctly agreeing with the singular subject "Economics." Options like "are," "were," and "have" are plural forms and would be grammatically incorrect in this context. This rule is essential for accurate subject-verb agreement with these specific types of nouns.