Acoherent narrative will be easy to follow and more enjoyable for your reader. using the context, the word "coherent" as it is used means interesting complicated connected detached

that’s the kind of bug henry was; and if we’d a had him along ’stead of our kings, he’d a fooled that town a heap worse than ourn done.”

the following key ideas correctly express the key sentence.

restate key idea: most people can learn to swim in ten short lessons.

restate key idea: the majority of water-accident victims require mouth-to-mouth breathing.

restate key idea: an empty, tightly closed gallon jug will support a tired swimmer.  

restate key idea: first aid is to prevent accidents as well as assist in rescue.

explanation: the key idea needs to have the same topic as the key sentence (drowning and safety).