—The dictionary is an important for students .Each of us must have one . —I think so .A.

问题补充：

—The dictionary is an important for students .Each of us must have one .

—I think so .

A. secret

B. tool

C. method

D. plan

答案：

A. secret

(答案→)B. tool

C. method

D. plan

解析：secret秘密; tool工具；method 方法；plan计划；句意：词典对于学生们来说是一个重要的工具。我们每个人都必须有一本。结合语境可知选B。