18. The computer program product according to claim 15 , wherein each of the test sentences is generated together with feature information obtained from the language model and a number of the variations of speech data is determined according to the feature information.
18. The computer program product according to claim 15 , wherein each of the test sentences is generated together with feature information obtained from the language model and a number of the variations of speech data is determined according to the feature information. 19. The computer program product according to claim 18 , wherein the feature information comprises a number of transitions to other words in the language model, a transition probability among words in the language model, or a combination thereof.