The correct answer is A. Circular.
Precast concrete piles are generally circular in shape because they are the most efficient shape for resisting bending and compression. They are also relatively easy to manufacture and transport.
Square piles are less efficient than circular piles because they have more surface area, which means they are more susceptible to cracking and damage. Octagonal piles are even less efficient than square piles because they have even more surface area. Square piles with corners chamfered are slightly more efficient than square piles, but they are still not as efficient as circular piles.
In addition to being more efficient, circular piles are also easier to manufacture and transport. They can be made in a variety of sizes and lengths, which makes them suitable for a wide range of applications. Square piles and octagonal piles are more difficult to manufacture and transport, which limits their use.
Overall, circular piles are the most efficient and versatile type of precast concrete pile. They are the best choice for most applications.