The InnoDB engine has a feature known as clustered indexes. Which three statements are true about clustered indexes as used in InnoDB?（）

• A、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