The correct answer is: Only I and II are implicit.
The statement “Do not lean out of the moving train” is a warning. Warnings are issued when there is a danger that someone might do something that could harm them. In this case, the danger is that someone might lean out of the moving train and get hurt.
The first assumption, “Such warnings will have some effect,” is implicit in the statement. If the railway authorities did not believe that the warning would have some effect, they would not have issued it.
The second assumption, “Leaning out of a moving train is dangerous,” is also implicit in the statement. The warning would not be necessary if leaning out of a moving train were not dangerous.
The third assumption, “It is the duty of railway authorities to take care of passengers’ safety,” is not implicit in the statement. The statement does not say anything about the duty of railway authorities. It is possible that the railway authorities have a duty to take care of passengers’ safety, but this is not something that can be inferred from the statement.
Therefore, the correct answer is: Only I and II are implicit.