Use IAM roles for cross-account access rather than sharing long-term credentials and Define policies with only the permissions required for each job function are correct because they implement temporary credentials and least privilege to reduce risk and limit access.

Use IAM roles for cross-account access rather than sharing long-term credentials is correct because roles issue temporary credentials through AWS Security Token Service and let trusted principals assume permissions without distributing static secrets. This practice reduces exposure from leaked credentials and supports rotation and auditing.

Define policies with only the permissions required for each job function is correct because applying least privilege confines identities to the minimal actions and resources they need and lowers the impact of compromised credentials. Scoped policies also simplify compliance reviews and make permission changes safer.

Grant AdministratorAccess to all identities to avoid permission errors is incorrect because granting broad administrative rights breaks least privilege and greatly increases the attack surface and blast radius for human error or account compromise.

Share the root user credentials only when critical billing needs arise is incorrect because the root account should not be shared and should be used sparingly. You should create IAM identities with appropriate billing permissions and protect the root account with strong controls.

Turn on MFA on the root account so multiple users can act as root without sharing the login is incorrect because enabling MFA strengthens root security but it does not provide a controlled way for multiple people to operate as root. You should delegate duties through IAM users, groups, and roles for auditable access.

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