Q19. Name the type of data structure where pointers are lined up such that the structure will form an upside-down tree in which a single node will be at the top and branches on left and right when...

Extracted text: Q19. Name the type of data structure where pointers are lined up such that the structure will form an upside-down tree in which a single node will be at the top and branches on left and right when going down the tree? Q20. Which type of data structure has indexed set of variables? Q21. Which type of data structure does not restrict the number of nodes or objects in a collection?