Final answer:
A system of interrelated ideas used to explain a set of observations is called a theory, which is a thoroughly tested and supported scientific explanation. The correct answer to the question is d. a theory.
Step-by-step explanation:
The question you are asking about is related to the concept of explaining sets of observations within a scientific context. Specifically, a system of interrelated ideas used to explain a set of observations is called a theory. A theory is a scientific explanation that has been repeatedly tested and supported by many experiments. In contrast, a hypothesis is a tentative explanation for scientific observations that can be tested. Therefore, the correct answer to your question is d. a theory.
A theory is not just a set of guesses; it represents a well-developed set of ideas that propose an explanation for observed phenomena. Theories are generally composed of multiple hypotheses that have been confirmed through repeated experimentation and can incorporate laws, which are often described mathematically. In the social sciences, theories are used to explain different aspects of social interactions and create testable propositions or hypotheses about society.