Answer : 4. "Both B & C"
Explanation :

Answer: D) Both B & C Explanation: The branch of biology that studies the different structures and functions of the cell is called Cell Biology or Cytology.  Cell biology (formerly called Cytology), is a Greek word: kytos, "vessel" is a branch of biology that studies the different structures and functions of the cell and focuses mainly on the idea of the cell as the basic unit of life. The cell (from Latin cella, meaning "small room") is the basic Structural, Functional (and)  Biological unit of all known living organisms.  A cell is the smallest unit of life that can replicate independently, and cells are often called the "building blocks of life".