[Q]: What is the missing first step of the following process: - Waste enters the kidneys - A processing moment in the kidneys let waste and fluid pass - Prevents larger molecules to pass - Fluid goes back to the bloodstream - Bad waste is removed - The final product is turned into urine.
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[A]: Fluid

[Q]: What is the missing first step of the following process: - The water freezes and thaws - Cracks form in the rocks - Cracks also form when rocks heat up - The rocks slowly break down.
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[A]: Water seeps into rocks

[Q]: What is the missing first step of the following process: - Rain picks up carbon dioxide as it falls to earth - The rain falls on the soil over the limestone - The carbon dioxide in the rain washes through the soil - The carbon dioxide turns into acid - The acid in the rain gets to the limestone below the soil - The acid dissolves the limestone - Acid continues to erode the limestone with more rain over time - The eroded limestone sometimes forms caves.
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[A]: Limestone is located under the soil

[Q]: What is the missing first step of the following process: - The liver uses enzymes to clean the blood - The cleaned blood is expelled - The liver creates bile from the items filtered - The liver takes energy and stores it as glycogen - The bile is sent to the intestines.
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[A]:
The liver takes in blood from the rest of the body