ExplanationThe sentence tells you that the selection of a fresh cause happens every five years, so the blank must refer to a word such as habit or custom. Ambivalence would indicate that the agencies are not sure about taking this action, and callousness indicate a lack of caring.
Wariness would indicate that they are hesitant to change the cause. Affectation is tricky because it sounds similar to affection, which might make it sound like a good choice. However, affectation actually means artificiality, which is not the meaning you need. Choices (B) and (D) are both good substitutes for custom are produce equivalent, appropriate sentences.
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