Cloud Guard helps improve the overall security posture of your tenancy in two primary ways. First, it monitors unauthorized or suspicious user activity, which helps in detecting potential security threats or breaches (option B). Second, it assists in identifying misconfigured resources, such as publicly accessible Object Storage buckets, instances, and restricted ports on security lists, which could pose security risks if left unrectified (option C). These functionalities help in maintaining and improving the security measures for your Oracle Cloud Infrastructure.