Question

a broad explanation for a wide range of situations and observations
theory
environmentalism
hypothesis

Explanation:

The definition "a broad explanation for a wide range of situations and observations" matches the scientific definition of a theory. A theory is a well - substantiated explanation of some aspect of the natural world that can explain many related observations and situations. Ethics is a branch of philosophy dealing with moral principles, hypothesis is a proposed explanation made on the basis of limited evidence (not broad), and environmentalism is a social movement or ideology focused on environmental protection, not a broad explanatory framework for various situations/observations.

Answer:

theory