参考答案

正确答案：C
解析：细节题型见第二段第一、二句：There are three main types of the influenza virus. The most important of these are type A and B，each of them having several subgroups.(这种流感病毒主要有三种类型。其中最主要的是A类和B类病毒，而每类病毒都有几种附属的亚病毒。)因此 C为答案。