Detailed Explanation:

Rationale for Correct Answers:

C. terraform.tfvars securely managed: Acceptable if distributed securely outside version control.

D. HCP Terraform/Terraform Cloud sensitive variables: Official best practice for team-based workflows.

E. Vault: HashiCorp Vault is designed for secret management and integrates well with Terraform.

Analysis of Incorrect Options:

A: Storing plaintext secrets on shared drives is insecure.

B: Checking secrets into version control is a major security risk.

Key Concept:Sensitive values should be managed securely in Vault, HCP Terraform, or securely shared .tfvars files — never in plaintext or version control.