[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 bird collects bits of sticks and grass - The sticks and grasses are placed between support branches - Leaves, mud and spider webs are added to the sticks - The mud, leaves and webs glue the sticks together - The solid nest supports the eggs -
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[A]: A bird picks a spot high spot, often in a tree

[Q]: What is the missing first step of the following process: - Food is chewed and mixed with saliva (spit) - Food travels down the esophagus (throat) - Food travels into the stomach - Acid in the stomach breaks the food down further - Food travels into the small intestine - Nutrients from food are absorbed into the blood stream - Food travels into the large intestine - Most of the remaining material is now waste - The waste is eventually removed from the body.
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[A]: Food is put into mouth

[Q]: What is the missing first step of the following process: - The blood travels into the neophrons - Waste is expelled via the neophrons - The waste goes to the bladder in the form of urine - The clean blood exits the kidneys.
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[A]:
Blood enters the kidney