The Model Risk Management (MRM) function in financial institutions is primarily responsible for reviewing and challenging models to minimize risks. This involves a thorough examination of the models to identify any potential issues or inaccuracies that could lead to significant financial losses or regulatory penalties. The MRM function also assigns models to different tiers based on their risk level. This tier-based system is crucial as it helps in prioritizing the models that require immediate attention and frequent validation. High-risk models, or those belonging to the top tier, are subjected to more frequent and detailed validation to ensure their accuracy and reliability. On the other hand, models with lower risk levels undergo less frequent validation. This approach allows the MRM function to effectively manage model risk by focusing their efforts on the models that pose the greatest risk to the institution.

Choice A is incorrect. While the MRM function does validate models, it does not do so every year regardless of their tier. The frequency of model validation is determined based on the risk level associated with each model, which is indicated by its assigned tier.

Choice B is incorrect. This statement incorrectly suggests that the MRM function does not consider the tier of a model when specifying the frequency of its validation. In reality, models are assigned to different tiers based on their risk level and this tier assignment plays a crucial role in determining how often they should be validated.

Choice D is incorrect. The MRM function's responsibilities extend beyond merely monitoring reports produced by model owners; they also actively review and challenge models to minimize risks and conduct validations as necessary based on each model's assigned risk level or tier.