The InnoDB engine has a feature known as clustered indexes. Which three statements are true about clustered indexes as used in InnoDB?（）
A primary key must exist for creation of a clustered index
B. A clustered index allows fulltext searching within InnoDB
C. The first unique index is always used as a clustered index and not a primary key
D. A clustered index provides direct access to a page containing row data
E. If no indexes exist, a hidden clustered index is generated based on row IDs
F. A primary key is used as a clustered index
G. A clustered index is a grouping of indexes from different tables into a global index for faster searching
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