The correct option is B Procambium
Procambium is a part of apical meristem that develops into primary vascular tissues, i.e. xylem and phloem. Protoxylem is the part of xylem that develops earlier during the growth of a plant. Metaxylem is the part of xylem that develops later. Tracheids are a type of cells present in xylem. Hence, the answer is procambium.