Option (C) Apical meristem is correct. According to the textbook context, virus particles have an uneven distribution throughout the plant body, and generally apical or axillary meristems are free from virus particles. Therefore, a very small part of apical meristems (less than 1 mm long) can be used as an explant to initiate cultures for the production of virus-free plants. This method has been successfully used for clonally propagated crops like sugarcane, banana, and potato. The other options (leaf segments, seeds, and stem cuttings) are not mentioned in the context as suitable for virus-free plant production.