The correct answer is B. Use shadow testing with continuous deployment.
Shadow testing is a deployment technique that involves routing a copy of the live traffic to a new version of the application, without affecting the production environment. This way, you can gather performance metrics and compare them with the current version, without exposing the new version to the users. Shadow testing can help you test against the full production load and identify any issues or bottlenecks before launching the new version. You can use continuous deployment to automate the process of deploying the new version after it passes the shadow testing.

The best options for defining triggers that indicate whether an incident requires a postmortem based on Site Reliability Engineering (SRE) practices are an external stakeholder asks for a postmortem and data is lost due to an incident. An external stakeholder is someone who is affected by or has an interest in the service, such as a customer or a partner. If an external stakeholder asks for a postmortem, it means that they are concerned about the impact or root cause of the incident, and they expect an explanation and remediation from the service provider. Therefore, this should trigger a postmortem to address their concerns and improve their satisfaction. Data loss is a serious consequence of an incident that can affect the integrity and reliability of the service. If data is lost due to an incident, it means that there was afailure in the backup or recovery mechanisms, or that there was a corruption or deletion of data. Therefore, this should trigger a postmortem to investigate the cause and impact of the data loss, and to prevent it from happening again.

According to SRE Workbook, one of potential SLI is as below:
* Type of service: Request-driven
* Type of SLI: Availability
* Description: The proportion of requests that resulted in a successful response.
https://sre.google/workbook/implementing-slos/