（複選）[4%] A database index is stored on disk. Minimizing disk I/O is important. Fan-out means the maximum number of children of a node. Please select all that are correct.
A A B-tree is suitable for disk because a node can store many keys and child pointers in one disk page/block. This gives high fan-out and small height (few page reads).
B A red-black tree is suitable for disk because its fan-out is 2, which reduces the number of disk page reads.
C A B+ tree is suitable for disk indexes for the same reason as a B-tree (high fan-out, small height).
D A B+ tree is often used when range queries are common, because its leaves can be linked for fast sequential scan on disk.
E For disk-based indexes, a red-black tree usually needs more page reads than a B-tree/B+ tree when searching for a key, because the tree is taller.
