1. [B+ tree] (20) Consider the following B+ tree (partly shown). Leaf nodes are linked (the links are not shown in the figure). The nodes are annotated with a label (e.g., "L1" for leaf node 1). Answer the following questions. 30 31 LI B 10 20 30 80 35 42 50 65 90 98 12 J3 68 69 70 79 L5 36 38 51 52 56 60 L2 L4 42 43 L3 98 99 100 105 LS 94 95 96 97 L7 81 82 L6 (1) Give the labels of all the nodes that need to be visited to answer the query: "find all records with search key at least 51". (2) Answer the same question, but for the query: "find the records with search key in [68, 100)". (3) Subtree C is not shown. What can we infer about the contents and shape of this subtree?