Pull request approvals are a feature in AWS CodeCommit that teams can use to enforce code review policies. By requiring a certain number of approvals before changes can be merged into a particular branch, like the master branch, teams can ensure that multiple team members have reviewed the changes. Branch protections in other services, such as GitHub, may offer similar functionality but are not the correct answer here because the scenario specifically involves AWS CodeCommit. The pre-signed commit policy is not applicable here, as it is not a feature of AWS CodeCommit. Lastly, the concept of 'stage locking' does not directly apply to Git-based version control systems and thus is incorrect in this context.