The correct option is D cambium
Based on the arrangement, vascular bundles are of two types.
1. Radial - Xylem and phloem are arranged separately in different radii and is found in roots of monocts and dicots.
2. Cojoint - Xylem and phloem are arranged together in the same radii and is found in stem and leaves.
Based on the presence or absence of cambium, vascular bundles may be
i. Open: A layer of cambium is present between the xylem and phloem.
ii. Closed: Cambium absent.