Ancient greek tragedy developed from religious ceremonies a need for entertainment aristotle’s philosophy dramatic competitions

often a noun phrase is just a noun or a pronoun:

people like to have money.

i am tired.

it is getting late.

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).