SQL & PL/SQL

Hi all,
I've this puzzle.

TableA and tableB

select max(a.ID_PART) 
from tableA a, tableB b 
where a.CDA_PART=b.CDA_PART
group by b.CDA_PART;

obtain ID_PART from A when match CDA_PART
The max() because may be multiple ID_PART for one CDA_PART... so I want the max value.

The problem comes when I put this subquery select into a INSERT statement that populate the B table with corrispondent max(ID_PART) on CDA_PART matching.

INSERT INTO tableC (ID_LOAD,  CDA_PART, ID_PART)
SELECT ID_LOAD, CDA_PART, (select max(a.id_part) from tableA a, tableB b 
                                          where a.CDA_PART=b.CDA_PART   
                                          group by b.cda_part)
FROM tableB
WHER ID_LOAD>5000;

the error message: ORA-01427: single-row subquery returns more than one row

I understand that select subquery returns multiple row, but I don't know how to correct the problem to insert for each CDA_PART of tableB the corrispondent max value of ID_PART of tableA

Any suggestions?