Problem: What is the missing first step of the following process: - Engines produce carbon dioxide - Living things produce waste - Waste decomposes - Decomposition produces methane - Water evaporates - Water vapor joins the atmosphere - Carbon dioxide, water vapor and methane are greenhouse gases -

A: People breathe and expel carbon dioxide

Problem: What is the missing first step of the following process: - Falls onto the ground - The acid rain starts scouring rocks - Destroys vegetation - The lack of vegetation alters the surrounding environment.

A: Acid rain is produced by chemicals that reach into the atmosphere

Problem: What is the missing first step of the following process: - The food is chewed - Saliva mixes with the food and starts breaking it down - The chewed food travels down the esophagus to the stomach - The stomach secretes acid - Grinds and mixes the food - The food moves to the small intestine - The small intestine uses enzymes to further break down the food - The food passes into the colon - The food is expelled from the body.

A: Food is taken into the mouth

Problem: What is the missing first step of the following process: - Release them into the air by process of sporulation - Spores are carried by the wind - Land in a hospitable growing environment - The spores germinate into the soil - The mushroom starts growing - The adult mushroom produce spores of its own to repeat the process.

A:
Adult mushrooms produce spores