Which of the following is not a source of metrics for Datadog?

The correct answer indicates that all listed options are indeed sources of metrics for Datadog. APM (Application Performance Monitoring) provides trace metrics that help monitor the performance of applications by capturing detailed execution traces. The numerous integrations, such as those with Docker, offer a plethora of metrics that can be used for monitoring various platforms and services. The Datadog Agent also plays a crucial role as it collects metrics from different sources, such as host metrics, logs, and application performance data.

Therefore, since APM, the integrations, and the Datadog Agent are all valid sources of metrics within the Datadog ecosystem, stating that "the above are all sources of metrics for Datadog" accurately reflects the capabilities of Datadog in gathering and managing metrics from diverse systems and applications.