needs to be tagged as containing a cause relation.
to find the most prevalent discourse relations for opinion summarization, we have used the tAC 2008 opinion summarization track input document set (collection) which is a subset of BLOG06 and the answer nuggets provided by tAC 2008 as the reference summary (or model summaries), which had been created to evaluate participants' summaries at the tAC 2008 opinion summarization track.