对于ORACLE PL/SQL标识符（Identifier）的有效长度是（）

A.v_record emp%type;
B.v_record emp%recordtype;
C.v_record emp%record_type;
D.v_record emp%rowtype;
E.v_record emp%row_type;

A.v_sal emp%rowtype;
B.v_sal emp.sal%type;
C.v_sal emp.sal.%type;
D.v_sal %type(emp.sal);
E.v_sal (emp.sal)%type;