| Query Difficulty, Robustness, and Selective Application of Query Expansion Recent countries visiting this post |  |
 | 4 | United States |
 | 1 | Russian Federation |
 | 1 | Spain |
| Query Difficulty, Robustness, and Selective Application of Query Expansion Recent countries visiting this post | |
| 4 | United States |
| 1 | Russian Federation |
| 1 | Spain |