Problem: What is the missing first step of the following process: - The stomach churns the food - With the aid of stomach acids - The food becomes a thick liquid - Is then passed to the small intestine.

A: Food leaves the esophagus and enters the stomach

Problem: 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.

A: Aluminium cans are put into a recycling bin

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: - May come from different sources - The gases remain trapped in the atmosphere - Through the suns light the gases hold in heat and energy - Trap them in our atmosphere - The earth may become warmer this way.

A:
Several types of gases form in the atmosphere