Explanation:

- In the passage, we need a word to describe how the papers are placed on the desk.

- Option 1: "tacked" - This means to attach something loosely. Papers are not usually "tacked" on a desk.

- Option 2: "slacked" - This isn't typically used to describe the arrangement of papers. It means to loosen or to avoid working.

- Option 3: "stacked" - This word means to arrange things in a neat pile. It fits well with how papers are usually organized on a desk.

- Option 4: "mounded" - While it can mean piling up, "mounded" usually implies a more casual or uneven heap, less appropriate for papers.

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