1. A learning support system which includes a computer including a processor and a memory, comprising: a question database in which a question to be asked of an answerer is stored; a learning history database in which a result of giving an answer to the question asked of the answerer, is recorded; a question generator for generating a question relating to a word changed in accordance with perturbation that changes a word, and stores the question in the question database; a question presentation module for asking the answerer the question extracted from the question database; an answer acquisition module for receiving the answer to the asked question; a scoring module for determining correctness or wrongness of the answer, by referring to the question database; and an achievement degree estimator for storing a result of the determination in the learning history database, wherein: the achievement degree estimator compares a number of types of perturbation within the questions to which a correct answer has been given with a predetermined learning threshold value; and the question generator generates a word changed in accordance with the perturbation of a different type in a case where the number of types of perturbation within the questions to which the correct answer has been given is smaller than the predetermined learning threshold value, and sets a question relating to the generated word as a candidate for the question.
1. A learning support system which includes a computer including a processor and a memory, comprising: a question database in which a question to be asked of an answerer is stored; a learning history database in which a result of giving an answer to the question asked of the answerer, is recorded; a question generator for generating a question relating to a word changed in accordance with perturbation that changes a word, and stores the question in the question database; a question presentation module for asking the answerer the question extracted from the question database; an answer acquisition module for receiving the answer to the asked question; a scoring module for determining correctness or wrongness of the answer, by referring to the question database; and an achievement degree estimator for storing a result of the determination in the learning history database, wherein: the achievement degree estimator compares a number of types of perturbation within the questions to which a correct answer has been given with a predetermined learning threshold value; and the question generator generates a word changed in accordance with the perturbation of a different type in a case where the number of types of perturbation within the questions to which the correct answer has been given is smaller than the predetermined learning threshold value, and sets a question relating to the generated word as a candidate for the question. 4. The learning support system according to claim 1 , wherein: the achievement degree estimator is configured to: refer to the learning history database, and compare a consecutive correct answer count with a predetermined consecutive-correct-answer threshold value; and perform a processing for comparing the number of types of perturbation within the questions to which the correct answer has been given with the predetermined learning threshold value in a case where the consecutive correct answer count is larger than the predetermined consecutive-correct-answer threshold value; and the question generator sets, when the consecutive correct answer count is equal to or smaller than the predetermined consecutive-correct-answer threshold value, the question relating to the word, which is of the same type of perturbation as the question to which the correct answer has been given and has different perturbation, as the candidate for the question.