117. A certain viral infection is widespread among children, and about 30 percent of children infected with the virus develop middle ear infections. Antibiotics, although effective in treating bacterial infections, have no effect on the virus. Yet when middle ear infections in children infected with the virus are treated with antibiotics, the ear often clear up.

Which one of the following most helps to explain the success of the treatments with antibiotics?

A. Although some types of antibiotics fail to clear up certain infections, other types of antibiotics might provide effective treatment for those infections.

B. Children infected with the virus are particularly susceptible to bacterial that infect the middle age.

C. Many children who develop middle ear infections are not infected with the virus.

D. Most viral infections are more difficult to treat than are most bacterial infections.

E. Among children not infected with the virus, fewer than 30 percent develop middle ear infections.

答案：B

A：否定原文。无关项

C：无关项

D：对原文的论断有相反的作用

E：无关项

问题是问：help to explain。那麽答案应该是顺着原文说的。

答案中middle age 是指中年人？ 那么在这里跟原文有什么关系？怎么理解B?