A B+-tree on an attribute X can be alternatively constructed in a batched manner: 1. Sequentially store the relation by sorting the records in a non-descending order of X; 2. Build the first-level index (the smallest key of each block in the index can be safely removed), then the second-level index, ..., until the top level has only one block. Consider 19 records inserted sequentially (not in ascending order) to a relation. The key values (in the order of the insertion) are 38,12,9,6,31,42,33,8,2,15,5,7,11,23,22,34, 27, 49, 50 respectively. Each block can hold up to 3 data records. Each block can hold up to 4 pointers together with 4 integers. Consider the two methods in building a B+-tree: a) Start with an initially empty B+-tree, insert the records sequentially. Draw the snapshots of the B+-tree after the insertion of 6, 7 and 50, respectively.