Which one of the following tissues in plants is usually without protoplast and regarded as dead cells?

Sclerenchyma is a mechanical/supporting tissue consisting of long, narrow cells with thick, heavily lignified secondary walls. At maturity these cells lose their protoplast (cytoplasm and nucleus) and become dead, providing rigidity and strength to plant parts. Parenchyma and collenchyma are living tissues with active protoplasts. Xylem parenchyma is also a living component of xylem (the dead components being tracheids and vessels). Hence sclerenchyma is the correct answer.