Read the reading below carefully, and then complete it with the best option A, B, C or D given below:
This article (1) ______ on the game of American football, a distinct type of football that developed in the United States in the 19th century. It developed out of two other sports, soccer (2) ______ known as association football) and rugby football, each of which remains a separate sport with its own specific set of rules. American football differs slightly in (3) ______ and field size from a style of football (4) ______ mostly in Canada, called Canadian football. Other varieties of the game popular in (5) ______ parts of the world are Australian football and Gaelic football.

This article (1) ______ on the game of American football, a distinct type of football that developed in the United States in the 19th century.