1. An information processing apparatus, comprising: an output unit for outputting a content, the content including at least audible data containing a plurality of vocabulary in a language; a receiving unit configured to receive a plurality of input operations from a learner based on the learner hearing at least some of the plurality of vocabulary in the output content; a recording unit configured to associate the plurality of vocabulary with a respective difficulty level determined for each of the plurality of vocabulary, and configured to store the plurality of vocabulary and the respective difficulty level, each of the plurality of vocabulary including a word, an idiom, or a phrase consisting of two or more words in the language; a registration unit configured to register a learning level, which is a degree of learning of the language to learn of the learner; calculating unit configured to calculate a respective frequency in use for each of the plurality of vocabulary, where each frequency is a respective number of times that a respective one of the plurality of vocabulary is used in the content; a specification unit configured to specify a subset of the plurality of vocabulary for learning by the learner according to the respective frequency in use and the registered learning level of the learner; and a control unit configured to analyze the plurality of input operations received by the receiving unit from the leaner during the outputting of the content, and registering only respective ones of the plurality of input operations that correspond with respective ones of the subset of the plurality of vocabulary.