Geomagnetic activity, the natural variations in Earth's magnetic field, it fluctuates in 11-year cycles.

地磁活动是地球磁场的自然变化，其波动周期为11年。

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Maybe they sense slight variations in the rate of change in the magnetic field, much like a hiker reads tightly spaced lines on a topographic map to discern a distinctive canyon.

也许它们感受磁场变化速度的细微变化，就像登山旅行者参照地形图上密密麻麻的线段以辨别一个与众不同的峡谷。

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Hint: it is recommended that teams design their robots to cope with variations in lighting and magnetic conditions, as these vary from venue to venue.

提示：鉴于各个场地的条件不同，建议各队设计好自己的机器人使其能够适应各种照明和磁场情况。

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