题目内容
“茶叶中提取咖啡碱”实验，升华过程中可打开漏斗观察咖啡碱生长过程，以便记录实验现象。
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升华是由化合物受热气化为蒸气，蒸气直接冷凝为固体的过程。
“茶叶中提取咖啡碱”实验，若实验操作顺利的话，可在滤纸上看到3~4mm长的白色略带黄色的针状结晶。
Traditionally, travel groups often hire ____to conduct their journeys, especially when the journeys are not too long.
Trains are ____to planes in that railway terminals are often in the centre of the destination while airports are often located 20 or 30 kilometers away from the centre.
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