The correct answer is:
(a) Environment – cognition
In the context of Cognitive Radio Architecture, the cognition cycle refers to the process in which the cognitive radio continuously monitors its environment, makes decisions based on this information, and then adapts its behavior or parameters (such as frequency, power, modulation schemes) to optimize performance. This cycle typically involves interactions between the environment (such as the radio frequency spectrum, interference, etc.) and the cognitive system's cognitive functions, which include sensing, reasoning, and decision-making.
Thus, the combination of Environment – cognition is what drives the cognition cycle, where the system adapts to and interacts with its changing environment.