You are presented with the quiz "chemical weathering causes iron to oxidize in what?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "chemical weathering causes iron in rock to oxidize" and "limestone is a fairly common rock type". So, what's the best answer to the question?
OPTIONS:
- calcite
- limestone
- In sediment
- the skin
- graptolites
- loose soil
- body water
- soils

Answer: limestone

You are presented with the quiz "What can have special excretory structures?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "some arthropods have special excretory structures" and "insects are the largest group of arthropods". So, what's the best answer to the question?
OPTIONS:
- barnacles
- animals
- feces
- molecules
- fungi
- cows
- insects
- planets

Answer: insects

You are presented with the quiz "what are living things that cannot make their own food?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "heterotrophs are living things that cannot make their own food" and "all animals are heterotrophs". So, what's the best answer to the question?
OPTIONS:
- hydrogen
- clouds
- animals
- humans
- bacteria
- bushes
- fungi
- plants

Answer:
animals