2. The annotation assisting apparatus according to claim 1 , wherein to estimate the candidate, the processor is configured to: generate, for each of the positions of the identified words, a sentence asking a word to fill the position of the word, by using a sequence of words around the position; give the generated sentence as an input to a question-answering system prepared in advance; and store a candidate word to be inserted to the position of the word in association with the position of the word in the non-transitory computer readable medium, based on the answer obtained from the question-answering system in response to the question sentence given from the question sentence input means.
2. The annotation assisting apparatus according to claim 1 , wherein to estimate the candidate, the processor is configured to: generate, for each of the positions of the identified words, a sentence asking a word to fill the position of the word, by using a sequence of words around the position; give the generated sentence as an input to a question-answering system prepared in advance; and store a candidate word to be inserted to the position of the word in association with the position of the word in the non-transitory computer readable medium, based on the answer obtained from the question-answering system in response to the question sentence given from the question sentence input means. 5. The annotation assisting apparatus according to claim 2 , wherein to estimate the candidate, the processor is further configured to: apply an analyzed sequence of morphemes as an input to another existing (zero-)anaphora resolver; receive a result of (zero-)anaphora resolution by the existing (zero-)anaphora resolver; and store the result of (zero-)anaphora resolution in the non-transitory computer readable medium.