We study the impact of using thesaurus-based query expansion methods at the Information Retrieval (IR) stage of a Question Answering (QA) system. We focus on expanding queries for questions regarding
, where verbs have a central role. Two different thesaurus are used: the OpenOffice thesaurus and an automatically generated verb thesaurus. The performance of thesaurus-based methods is compared against what is obtained by (i) executing
and (ii) applying a simple query generalization method. Results show that thesaurus-based approaches help improving
at retrieval, while keeping satisfactory
. However, we confirm that positive impact for the final QA performance is mostly achieved due to increase in
, which can also be obtained by using simpler methods. Nevertheless, because of its better relative precision thesaurus-based expansion is effective in selectively reducing the number of
text passages retrieved, thus reducing computational load in the answer extraction stage.