What is the length of a running train P crossing another running train Q? I. These two trains take 18 seconds to cross each other. II. These trains are running in opposite directions. III. The length of the train Q is 180 metres.

• I. These two trains take 18 seconds to cross each other.
• II. These trains are running in opposite directions.
• III. The length of the train Q is 180 metres.
• A. I only
• B. II only
• C. III only
• D. All I, II and III are required
• E. Even with I, II and III, the answer cannot be obtained.