Explanation:

The xylem is a specialized tissue in plants that is responsible for the transport of water and minerals from the roots to the rest of the plant. It is composed of several types of cells, each with a specific function.

Xylem Parenchyma:
- Xylem parenchyma is a type of xylem cell that functions in storage and lateral conduction of water and minerals.
- It is living and has thin cell walls.
- It is found in the pith of stems and in the cortex of roots.
- Xylem parenchyma cells have large vacuoles that can store water and nutrients.

Tracheids:
- Tracheids are elongated, dead cells with tapered ends.
- They are the most primitive type of xylem cells.
- They have thick secondary cell walls with pits and lignin deposits.
- Tracheids are responsible for water transport and support in plants.
- They are found in all vascular plants.

Vessels:
- Vessels are another type of xylem cell that is involved in water transport.
- They are larger and more efficient than tracheids.
- Vessels are formed by the fusion of many individual cells called vessel elements.
- They have perforations in their end walls called perforation plates, which allow for efficient water movement.
- Vessels are found in angiosperms and a few gymnosperms.

Companion Cells:
- Companion cells are a type of phloem cell, not xylem cell.
- They are closely associated with sieve tube elements in the phloem.
- Companion cells provide metabolic support to the sieve tube elements by supplying them with nutrients and energy.
- They are living cells with dense cytoplasm and many mitochondria.

Conclusion:
The correct answer is option B, Companion cells. Companion cells are not a type of xylem cell, but rather a type of phloem cell that functions in metabolic support for sieve tube elements. Xylem parenchyma, tracheids, and vessels are all types of xylem cells involved in water and mineral transport in plants.

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