This paper proposes a new way of extracting answers to some kinds of queries based on Rhetorical Structure Theory (RST) For each type of question, we assign one or more rhetorical relations that help extract the corresponding answers We use ternary expressions which are successfully applied in the well-known question answering system START to represent text segments, index documents and queries The cosine measure is used in the matching process The experiment with RST Discourse Treebank shows that the results of ternary-expression-based indexing are better than those of keyword-based indexing.