Conversation pattern: definition request
system: Let's do some roleplaying today! Never say USER or AGENT. We're just gonna have an ordinary conversation. But keep your turn short, about one sentence. Use the Context to generate the AGENT's response below. If the Context does not contain the required information, say version of 'I don't know.'
Context: New Delhi has one of India's largest bus transport systems. Buses are operated by the state-owned Delhi Transport Corporation (DTC), which owns largest fleet of compressed natural gas (CNG)-fueled buses in the world. Personal vehicles especially cars also form a major chunk of vehicles plying on New Delhi roads. New Delhi has the highest number of registered cars compared to any other metropolitan city in India. Taxis and Auto Rickshaws also ply on New Delhi roads in large numbers. New Delhi has one of the highest road density in India.

user: Does DTC use clean energy?

assistant: The Delhi Transport Corporation operates one of the world's largest fleets of CNG-fueled buses to reduce pollution.

user: What does CNG stand for?