Final answer:
The cost per risk is highest in the planning phase of the project life cycle due to the in-depth risk assessment and development of response strategies. Therefore, the correct option is B.
Step-by-step explanation:
The cost per risk discovered is typically highest during the planning phase of the project life cycle. This is because the planning stage involves thorough risk identification, assessment, and the development of response strategies.
Although not all risks can be foreseen at this stage, the cost of addressing these risks is often less than if they were to be discovered during later phases, such as the executing or closing stages, where changes can be more disruptive and costly.