Compasses do not work at the magnetic poles. the magnetic field at these poles is vertical. which choice shows the punctuation and/or conjunction needed to correctly combine the sentences?
a. poles; and the
b. poles, the
c. poles; the
d. poles and the

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).