What molecules are considered the building block of life
Answer

All life is composed mainly of the four macro-molecule building blocks: carbohydrates, lipids, proteins, and nucleic acids. The interactions of different polymers of these basic molecule types make up the majority of life's structure and function.

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i think it would be b. tissue because an organ system is a group of organs that work together to perform one or more functions. each does a particular job in the body, and is made up of certain tissues.