Final answer:
Good psychological theories must be testable, falsifiable, and parsimonious. Complexity is not required for a theory to be considered robust; therefore, the correct answer is that theories do not need to be complex.
Step-by-step explanation:
Good psychological theories should possess several important properties to be considered scientifically viable. Among these properties, theories must be testable, meaning they can be empirically examined through experimentation or observation. Additionally, a valuable characteristic of a theory is being falsifiable; that is, there must be a possibility to prove the theory wrong through empirical evidence. Theories should also be parsimonious, which means they should be as simple as possible while still explaining the phenomena in question. However, one property that is not essential for a good psychological theory is complexity. Theories that are overly complex may lack clarity and can hinder understanding and testing. Therefore, the correct answer to the question is (c) Complex, as good psychological theories do not need to be complex to be considered robust and reliable.