To ensure that the build history clearly displays the stage at which the build failed, it's essential to have separate steps for each task in the Cloud Build configuration. This approach allows for granular visibility into the build process, making it easy to identify exactly where a failure occurred. Option D is the correct choice because it involves creating a Cloud Build build config file with separate steps for compiling and executing unit and integration tests. This method ensures that if any step fails, the build history will clearly indicate the specific stage of failure, unlike the other options which either combine steps or do not provide clear failure stage identification.