Question

according to the cell theory, which structure contains cells?
blood
water
carbon dioxide
chromosome

Explanation:

To solve this, we analyze each option using cell theory (all living things are made of cells, cells are basic unit of life, new cells from pre - existing cells).

• Blood: It is a tissue in animals, and tissues are made of cells. Blood contains red blood cells, white blood cells, etc.
• Water: It is a non - living substance, a chemical compound ($H_2O$), and has no cells.
• Carbon dioxide: It is a gas ($CO_2$), non - living, and has no cells.
• Chromosome: It is a structure within a cell (in the nucleus), made of DNA and proteins, and is not a structure that contains cells (it is part of a cell).

So blood is the structure that contains cells.

Answer:

A. blood