A life or living being is made of fundamental building blocks, quite like a house is made of bricks.
Atom (A) is the building block of all matter. It is made of a nucleus core and electron periphery. There are several types of atoms like Hydrogen, Oxygen, Carbon, etc.
Organelles (B) are subunits of cells. Mitochondria, Golgi apparatus, etc. are examples of cellular organelles.
DNA (D) is a macromolecule or biopolymer responsible for the transmission of hereditary information. These are composed of a nitrogenous base, a sugar and phosphate moieties.
Therefore, the options A, B & D are incorrect.
Cells (C) are the fundamental building blocks of life that are independent but associate to form complex tissues and organs. Cells are defined as the smallest structural and functional unit of an organism. An organism may be unicellular or multicellular. A cell is composed of a membrane that encloses a cytoplasm which has several cellular organelles distributed within.
Therefore, option (C) is correct.