单选题 Currently, the number of first-time admissions of individuals diagnosed as manic-depressives to hospitals in Great Britain exceeds by nine times the number of admissions of such patients to public and private hospitals in the United States, even though the population size of the United States is many times that of Great Britain.
Which of the following, if true, would be most useful to an attempt to explain the situation described above?

【正确答案】 A
【答案解析】