You are presented with the question "What do things that cannot make their own food need as a nutrient?" and the following answer choices: 
- Energy
 - metal
 - animals
 - mud
 - Energy.
 - protein
 - prototype
 - fungi

Now knowing that heterotrophs are living things that cannot make their own food and proteins are an essential nutrient for heterotrophs , choose the best answer.


 

      protein   