I know no one will answer this question correctly but if someone does I just wanna give you a big thanks! Which part of a thermometer responds to changes in temperature? Describe how it responds when the air in the bottle (a) warms up (b) cools down.

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but i think it is 2

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).