Photo #1 (an assembly of some kind): The photographer uses balance and symmetry to some degree because they chose to place the building in the middle of the picture with the roughly the same amount of protestors on each side, and I'd say they used contrast as well because of the difference in the earth tones of the background and the more bright, vivid colors of the foreground. This picture also demonstrates the concept of space.
Photo #2 (ladies on a bike): The photographer used depth of field, pattern (the horsemen in the background), and emphasis with the two ladies in the foreground.
Photo #3 (up-close of some dude): The photographer used emphasis obviously with the extreme close-up of this guy's face, and some balance and symmetry with a pretty evenly angled photo of his face.
Photo #4 (classroom with blue desks): The photographer used an interesting angle to take the photograph, contrast in the darkness of the room and the brightness of the desks, and a pattern to some degree of the bright blue desks.
