Statement: "Do not lean out of the moving train," a warning displayed in a railway compartment.\nAssumptions:\nI. Such a warning will have some effect on passenger behavior.\nII. Leaning out of a moving train is dangerous.\nIII. It is the railways’ duty to take care of passengers’ safety.

Introduction / Context:
Public safety warnings are issued to reduce risk. The instruction “Do not lean out of the moving train” aims to prevent harm. Which beliefs must be true for such a warning to be meaningful?

Given Data / Assumptions:

• A formal warning by the railway authority.
• No explicit claim that warnings always change behavior.
• Implied safety mandate of the railways.

Concept / Approach:
A safety warning presupposes (a) the act is dangerous and (b) the issuer is responsible for passenger safety. Belief about guaranteed effectiveness is not necessary; authorities may warn even if some ignore it.

Step-by-Step Solution:
1) Without II (danger), the warning would lack rationale; hence II is necessary.2) Without III (duty of care), the railway’s role in issuing such warnings would be ungrounded; warnings arise from safety obligations.3) I (effectiveness) is helpful but not required; warnings can be justified even if compliance is uncertain.

Verification / Alternative check:
Regulators issue warnings despite imperfect compliance; their duty and the hazard justify doing so.

Why Other Options Are Wrong:

• I and II: Omits the safety-duty basis for issuing warnings.
• Only II: Ignores institutional responsibility.
• All three: Overstates necessity by including guaranteed effect.

Common Pitfalls:
Equating “worth issuing” with “certain to work.”

Final Answer:
II and III are implicit.