How many times does something need to be repeated to be remembered?

The principal effector function of igm is

Read the paragraph and answer the question that follows: the town of belmond, iowa, needs to add weather sirens. the loud and steady wail would warn citizens of approaching danger. if past history is an indication, the sirens will save hundreds of lives. with a prediction of a deadly storm season, the alert which sentence should be revised to eliminate redundancy? the town of belmond, iowa, needs to add weather sirens. the loud and steady wail would warn citizens of approaching danger. if past history is an indication, the sirens will save hundreds of lives. with a prediction of a deadly storm season, the alert system is needed immediately.

Are people more motivated to change from positive or negative experiences, like slavery, womens rights, and any other historical movements/moments? i need more factual information than opinions.