Option 3 : Assumptions I, II and Ill all are implicit.
- The use of a warning implies that the action of leaning out of the moving train is harmful. Therefore, assumption 1 is implicit.
- The authorities would put up a warning only if they believe that it can restrain people from leaning out of a moving train. Therefore, assumption 2 is implicit.
- As the warning was posted in the railway compartment, it is implicit that passengers' safety is the responsibility of the railway authorities. Therefore, assumption 3 is implicit.
Hence, "Assumptions I, II and Ill all are implicit." is the correct answer.