Which of the following is an example of a movable obstruction?

A movable obstruction is defined in the Rules of Golf as an obstruction that can be moved without causing damage to it or the course. Clubs are considered movable obstructions because they can be easily picked up and relocated by a player without causing harm. This aligns with the principle of flexibility in play, allowing golfers to perform shots without interference.

Tree roots and stakes, on the other hand, are considered immovable obstructions. Tree roots are part of a larger structure and cannot be moved without damaging the tree or the surface, which preserves the integrity of the course. Stakes, which are used to define areas of the course, are also fixed in place and cannot be moved without changing the course's layout. Loose impediments, while they can be removed, are not categorized as movable obstructions in the same context, as they are typically natural elements such as leaves or twigs that are not fixed to the ground.

Thus, clubs fitting the definition of a movable obstruction is the reason this answer is correct.