The correct answer is B. 10-20 minutes.
In the dry phase of heating bamboo poles, they are typically heated to remove moisture and make them more durable. Given the temperature range between 490°C and 540°C, the heating process must be efficient to ensure uniform drying and minimal damage to the bamboo.
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Heating at high temperatures like 490°C to 540°C can rapidly remove moisture. The goal is to achieve uniform heating without causing structural damage or charring the bamboo.
- 5-10 minutes (Option A) might be too short to ensure uniform heating and complete drying, especially for thicker poles.
- 20-30 minutes (Option C) or 30-40 minutes (Option D) might be excessively long, risking damage to the bamboo structure or even causing it to ignite due to the high temperatures.
Therefore, 10-20 minutes is a balanced duration that allows for thorough, uniform heating and drying of bamboo poles within the specified temperature range.