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KaplanThe detour road sign but tells you that you can expect a change of direction in the sentence. The first half of the sentence describes a problem —conflict between generations— which does something in response to changes in social and economic conditions. The shift in the sentence turns on the words nature and intensity; these are the aspects of the problem that will be affected by change. Try constructing a paraphrase to convey this shifting problem. For example: Conflict between generations persists for centuries, but the nature of the conflict differs in response to changing conditions.
You need a word that conveys a shift in intensity and nature.
Scan the answer choices to look for a word that resembles your prediction. All of the given choices convey some type of change. DISAPPEAR, DECLINE, and WANE (to get smaller or weaker) all convey a reduction of intensity. Although you know there will be a change in the problem, nothing in the sentence indicates that the problem will decrease. You are looking for a more neutral term. By this logic, you can also eliminate INCREASE, which suggests the problem has worsened. Only VARY provides a neutral expression of change.
Conflict between generations might be a problem that has persisted for centuries, but the nature and intensity of the conflict obviously vary in response to changes in social and economic conditions.