—The dictionary is a useful for understanding new words. —I think so. A. secret B. tool C

问题补充：

—The dictionary is a useful for understanding new words.

—I think so.

A. secret B. tool C. way

答案：

解析：本题表示的含义是字典是理解新单词的有用工具，tool是工具的意思，与题意相符，故本题选B。