A、The scientists tested them in the medical center. B、The blind infants were visited by research workers every two weeks. C、The

A special research team organized and dispatched from the local medical center performed experiments on the completely blind infants. The test sample included twenty completely blind infants, who lived at home with their mothers or family. The research workers would visit the infants and closely observe the developments of their sense and behavior every two weeks.
    In most cases, the research workers tested the response of the blind infant to different stimuli common in the family environment. Generally speaking, a normal baby would react with smiles and laughter to tickling, to the voice of a relative, and to hugging from his family. His reactions were swift and fleet. Nevertheless, most of the blind infants, according to the experiments, responded to stimuli impassively. In fact, they were apathetic and indifferent to any sound. But under some special circumstances, some of them were able to react to the sound of their mothers with a smile. Usually, then-response was very slow and phlegmatic.
   The tests were conducted over a nine month period, and they began when the blind infants were one month old and ended when they were ten months old.
Questions 21-25 are based on the passage you have just heard.
21. Which of the following statements is true?
22. How were the experiments conducted?
23. What can we learn about the blind infants according to the passage?
24. Which of the following formed the special research team?
25. How about the blind infants’ behavior?