If you write a sentence with an unclear antecedent, it means you used

a. a plural pronoun when a singular pronoun was needed.
b. a possessive pronoun instead of a subject pronoun.
c. an object pronoun instead of a possessive pronoun.
d. a pronoun that could refer to more than one person, place, or thing.

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).

need answers now

which of franklin’s “virtues” is the main idea of the aphorism?

don’t throw stones at your neighbor if your windows are glass.

cleanliness

tranquility

chastity

humility