.Don’t make jokes in America. Even in experienced hands, a joke can be a dangerous thing. I came to this ______ recently while passing through Customs and Immigration in Boston..

A．decision

B．position

C．conclusion

D．illusion

微生物包括：（）细胞结构不能独立生活的病毒、亚病毒（类病毒、拟病毒、朊病毒）；具细胞结构的真细菌、古生菌；具（）细胞结构的真菌（酵母、霉菌、蕈菌等）、单细胞藻类、原生动物等。