Which type of the following cells is thin-walled and living at maturity?

The correct answer is collenchyma. Collenchyma cells are elongated cells with unevenly thickened cell walls, which provide support to growing plant organs. They are living at maturity and have thin walls compared to other types of cells such as sclerenchyma cells. Sieve tubes and xylem vessels are specialized transport cells in plants, while sclerenchyma cells are specialized for support and protection.