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Which three statements are true regarding single-row functions？（）
A: They can accept only one argument.
B: They can be nested up to only two levels.
C: They can return multiple values of more than one data type.
D: They can be used in SELECT， WHERE， and ORDER BY clauses.  
E: They can modify the data type of the argument that is referenced.
F: They can accept a column name， expression， variable name， or a user-supplied constant as arguments.

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出自：Oracle认证

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