2. The information processing system according to claim 1 , wherein the extraction instructions are further configured to cause at least one of said at least one processor to count the degree of co-occurrence of content words contained in the one posted sentence and thereby obtain a score of the one posted sentence, and then extract the posted sentence with the score of equal to or more than a specified threshold.
2. The information processing system according to claim 1 , wherein the extraction instructions are further configured to cause at least one of said at least one processor to count the degree of co-occurrence of content words contained in the one posted sentence and thereby obtain a score of the one posted sentence, and then extract the posted sentence with the score of equal to or more than a specified threshold. 3. The information processing system according to claim 2 , wherein the extraction instructions are further configured to cause at least one of said at least one processor to output posted sentences with the score of equal to or more than the specified threshold in a descending order of the score.