SSH traffic is not allowed in the security list nor on the NSG from the Internet is the correct answer. This is because the security list only allows ingress traffic from 10.0.0.24 on port 22, and the NSG only allows ingress traffic from 10.0.0.0/16 on port 22. Neither of them allows ingress traffic from 0.0.0.0/0 (the Internet) on port 22, which is required for SSH access. The other options are not correct, as they do not explain why SSH access is not possible. References: [Security Lists], [Network Security Groups]

The explanation is that shielded instances are VM instances that have additional security features to protect them from low-level threats, such as rootkits and bootkits that can infect the firmware and operating system and are difficult to detect. Shielded instances use verified boot, which ensures that only trusted software components are executed during the boot process. Shielded instances also use virtual trusted platform module (vTPM), which provides a secure storage for encryption keys and certificates. Shielded instances are available for Oracle Linux 8 platform images with VM.Standard2.* shapes.

According to the Oracle Cloud Guard documentation1, Cloud Guard is a cloud native service that helps customers monitor, identify, achieve, and maintain a strong security posture on Oracle Cloud. Use the service to examine your Oracle Cloud Infrastructure resources for security weakness related to configuration, and your Oracle Cloud Infrastructure operators and users for risky activities. Upon detection, Cloud Guard can suggest, assist, or take corrective actions, based on your configuration.

Therefore, option A and option E are correct ways that Cloud Guard helps improve the overall security posture for your tenancy. Option B is incorrect because Cloud Guard does not allow you to centrally manage encryption keys. That is the function of the Vault service2. Option C is incorrect because Cloud Guard does not prevent you from creating misconfigurations on your resources in OCI. It only detects and reports them, and optionally takes corrective actions. Option D is incorrect because Cloud Guard does not mask sensitive data and monitor security controls on your Oracle databases. That is the function of the Data Safe service3.