Problem: Given the question: What is the missing first step of the following process: - The water combines with carbon dioxide in the air to form carbonic acid - As the acid is formed, the iron starts to dissolve - Some of the water breaks down into hydrogen and oxygen - The free oxygen and dissolved iron bond together - They form iron oxide, which is rust -
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The answer is:
Water comes into contact with something made of iron

Problem: Given the question: What is the missing first step of the following process: - Aluminium cans are then collected and taken to a treatment plant - At the treatment plant the aluminium is sorted and cleaned - Readied for reprocessing - The aluminum cans go through a re-melt process - Turned into molten aluminium - The molten aluminum is made into large blocks called ingots - The ingots are sent to mills and are rolled out into thin sheets - The rolls are ready to be made into new aluminum products.
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The answer is:
Aluminium cans are put into a recycling bin

Problem: Given the question: What is the missing first step of the following process: - The seeds are dispersed by wind, animals, etc - The seeds reach the ground - Grow into new trees - These new trees produce seeds - The process repeats itself over and over -
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The answer is:
A tree produces seeds