单选题 The successful attempt to save a badly bitten boy in 1885 was based on the theory that______.

A、 infective agent of rabies could be used for vaccination
B、 a series of injections of new virus could make people resistant to rabies
C、 the infective agent of rabies could be recovered from the infected body
D、 the longer incubation period would enable human body to build up enough resistance

【正确答案】 D

【答案解析】推断判断题。第四段的倒数第二句提到疫苗应用的理论依据是：如果狗在两周内因注射疫苗而受到保护的话，那么人体更长的疾病潜伏期可使人通过疫苗在狂犬病发作之前在体内形成保护机制。只有选项D是对这一理论的概括。