In the following passage, some words have been deleted. Read the passage carefully and select the most appropriate option to fill in each blank.

There is always something so fascinating about trains and journeys. There (1) ______ certain symbols and signages inside and outside of the train. The (2) ______ of most of them might not be known to everyone. (3) ______ you are a frequent traveller or not, you may have (4) ______ the letter X or a cross mark on the back of the last (5) ______ of the train.

Select the most appropriate option to fill in blank number 4.