The best deployment strategy for UC to use in this environment is to refresh the developer's sandbox, develop changes, refresh the common sandbox, deploy to the common sandbox, test changes, as this will ensure that the developer's sandbox has the latest production data and metadata, and that the common sandbox has the latest production data and metadata as well as the developer's changes, before testing and deploying to production. Option B is not correct, as refreshing the developer's sandbox after testing the changes will erase the changes and make them unavailable for deployment to the common sandbox. Option C is not correct, as refreshing the developer's sandbox after developing the changes will erase the changes and make them unavailable for deployment to the common sandbox. Option D is not correct, as refreshing the common sandbox before developing the changes will make the common sandbox out of sync with the production data and metadata.

The architect should suggest the following actions to help UC discover the failing unit tests earlier: Train the administrators to make their changes in a special "admin changes" sandbox, and then promote to production, and ensure a metadata backup is committed to version control every day and a diff published to the release team. Training the administrators to use a sandbox can help prevent direct changes to production that can break the code or the unit tests. Ensuring a metadata backup and a diff can help identify any changes that have been made to production and compare them with the source of truth.