The correct option is D both b and c
When cambium is absent in the vascular bundle, it is called closed. Closed vascular bundles are seen in monocots and in leaves of both monocots and dicots.
Cambium helps in secondary growth. As cambium is absent, there is no secondary growth observed in monocot plant parts and also in dicot and monocot leaves.
Vascular bundles are said to be open in the dicot stem as they have cambium.