In Robinson and Mitchell's (1992) Study, How Can We Be

In Robinson and Mitchell's (1992) study, how can we be confident that children gave the right answer for the right reason?

A) Because they interpreted the request literally when the speaker held a true belief
B) Because they seemed to be concentrating very hard and were attending to the task
C) Because they understood the question
D) We can't
E) The children said they were certain that they had made a correct judgment