Which is the smallest part of an organism? A. body tissue

B. organ system

C. organ

D. cell

D. cell

The cell is the smallest structural and functional unit of living organisms, which can exist on its own. Therefore, it is sometimes called the building block of life. Some organisms, such as bacteria or yeast, are unicellular—consisting only of a single cell—while others, for instance, mammalians, are multicellular.

Explanation:

there ya go mate ^^

D. cell is the smallest part of an organism.

as cell is basic functional and structure of life.

biology is the study of life. it is the study of living organism.

that is wrong, its not thymus.