Problem: 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.

A: Water seeps into rocks

Problem: What is the missing first step of the following process: - Causes them to absorb aluminum from soil - The water runs off from the soil into lakes, streams, etc - Fish and their eggs die - Frogs and plants die - Insects and other wildlife die - The ecosystem is out of balance, causing further problems -

A: Acid rain makes waters acidic

Problem: What is the missing first step of the following process: - The oxygen travels into the body - Breaks down into glucose - Carbon dioxide is produced by the glucose breakdown - The carbon dioxide is exhaled out of the body through the nose or mouth.

A: A person takes in oxygen through their nose or mouth

Problem: What is the missing first step of the following process: - Blood is carried to the kidneys through the renal arteries - The kidneys contain filters inside - The filters capture the waste products - The waste is combined with water to make urine - The urine leaves the kidney and is collected in the bladder - The cleaned blood is returned to the body.

A:
Waste products are deposited in the blood