Suppose we have a B-tree 3 nodes with room for 3 keys and 4 pointers. suppose also that when we split a leaf, we divide the pointers 2 and 2. while when we split and interior node, the first three pointers go with the first node(left node), and the last two pointers go with the second node(right node). we start with the leaf containing pointers to record with keys 1 2 and 3. we then add in order, record with the keys 4,5,6 and so on. At the insertion of what key will the B tree first reach four levels???