Explanation:

- In many countries, a difference in pay between men and women is a well-known issue.

- Option 1: Unlikeliness - This refers to something that is improbable or not expected. It doesn't fit the context of discussing known issues in wage equality.

- Option 2: Equivalence - This means being equal or the same, which contradicts the idea of a pay gap.

- Option 3: Disagreement - While it refers to a lack of consensus, it doesn’t directly address the issue of unequal pay.

- Option 4: Disparity - This indicates a great difference between things, which fits the context perfectly when discussing pay differences.

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