Which of the following elements can be changed according to the laws of the game?

The size of the field can be modified according to the laws of the game within certain parameters set by governing bodies. The Laws of the Game, as established by the International Football Association Board (IFAB), specify minimum and maximum dimensions for soccer fields, allowing for variations in size based on the level of play and age of the players.

For instance, a youth soccer match may have a smaller field than one for adult players. It's essential to maintain the integrity of the game while still accommodating various playing conditions, thus making field size one of the more flexible elements in the regulations.

Other elements, such as the height of the goal posts, the number of players on the field, and the match duration, are strictly defined and cannot be altered without affecting the fundamental nature of the game. The height of the goal posts and number of players are established to ensure a standardized playing environment, while match duration is set to regulate the flow of the game and provide a fair contest.