Read the excerpt from The Dark Game.

As a result of the cut cables, Germany lost its most secure long-distance communications system. The Germans now had to rely on radio transmissions from their powerful wireless station at Nauen, a few miles from Berlin. Which was exactly what the British military knew they would have to do. And once the Germans began sending wireless messages, MI8, the British code breakers, began plucking them from the air. Of course, all German correspondence was sent in a complicated cipher system, so that was when the hard work began for the code breakers of MI8.

Which type of structure is used in the text?

problem and solution
cause and effect
chronological
comparison and contrast