Multi-tenancy within the same database (B) presents the greatest risk of data leakage in the cloud environment, because it means that multiple customers share the same physical database and resources. This can lead to data isolation and security issues, such as unauthorized access, cross-tenant attacks, or data leakage due to misconfiguration or human error. To prevent data leakage in a multi-tenant database, cloud providers need to implement strict access control policies, encryption, isolation mechanisms, and auditing tools.

Lack of data retention policy (A) is not the greatest risk of data leakage in the cloud environment, because it mainly affects the availability and compliance of data, not its confidentiality or integrity. Data retention policy defines how long data should be stored and when it should be deleted or archived. Without a data retention policy, cloud customers may face legal or regulatory issues, storage costs, or performance degradation.

Lack of role-based access © is not the greatest risk of data leakage in the cloud environment, because it can be mitigated by implementing proper authentication and authorization mechanisms. Role-based access control (RBAC) is a security model that assigns permissions and privileges to users based on their roles and responsibilities. Without RBAC, cloud customers may face unauthorized access, privilege escalation, or data misuse.

Expiration of security certificate (D) is not the greatest risk of data leakage in the cloud environment, because it can be easily detected and renewed. A security certificate is a digital document that verifies the identity and authenticity of a website or service. It also enables secure communication using encryption. If a security certificate expires, it may cause trust issues, warning messages, or connection errors, but not necessarily data leakage.