The correct option is
D cambium
Vascular bundles include the complex tissues: xylem and phloem. Open vascular bundles are seen in the stem of the dicot plants such as mustard, legumes, etc. Such vascular bundles, possess the ability to form secondary xylem and secondary phloem tissues.
Absence of cambium between xylem and phloem, forms closed vascular bundles. No secondary tissues are formed. They are seen in roots and stem of monocots such as grasses and sugarcane plants.
Ground tissue includes all the tissues except epidermis and vascular bundles. It is made up of simple tissues such as parenchyma, collenchyma and sclerenchyma. In stems and roots, these tissues form the cortex, pericycle, pith, medullary rays.
Pith is composed of parenchyma cells. Its function is storage of nutrients in young plants.
Conjunctive tissue is a parenchymatous ground tissue that is present in the vascular bundles of the root.