Docker Compose: Find the Backend Service

A web frontend can't reach its backend. In Compose, services talk to each other by SERVICE NAME (Docker's internal DNS). /root/project/task.txt names the frontend service (it differs per session). Examine /root/project/docker-compose.yml, find the service THAT frontend depends on, and record its service name to /root/answers/backend.txt. Other services depend on other things — read the right block.