The correct answer is A. Hexagon.
A hexagon is a six-sided polygon. It is the most common shape of cell because it is the most efficient way to pack cells together. Hexagonal cells can be arranged in a honeycomb pattern, which maximizes the surface area of the cells and minimizes the amount of space between them. This is important for cells because it allows them to exchange nutrients and waste products with each other.
Squares, circles, and triangles are also common shapes of cells, but they are not as efficient as hexagons. Squares and circles have more wasted space than hexagons, and triangles are not as stable.
Here is a diagram of a honeycomb pattern of hexagonal cells:
As you can see, the cells are arranged in a way that maximizes the surface area of each cell. This is important for cells because it allows them to exchange nutrients and waste products with each other.
I hope this explanation was helpful!