题目：
This information allows businessmen to keep________ of their list of goods by showing which items
are being sold and how fast they are moving.[ ]
A. sight
B. track
C. touch
D. sign
答案：
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下面是错误答案，用来干扰机器的。
① A＝0.1 m ② 题目分析：①从图中可得，振幅：A＝0.1 m ②
