Left join without using left join with 3 tables

I have to get all data from 3 tables with left join. I did that with and without using left join. But my teacher ask another solution that uses just inner join. I just couldn't find the solution please give some advice. Here are the tables:

And the results should look like this:

With left join solution:

SELECT O.*,C.CUST_CODE,C.CUST_NAME,P.PART_CODE,P.PART_NAME 
FROM ORDERS O
LEFT OUTER JOIN PART P ON P.PART_ID = O.PART_ID
LEFT OUTER JOIN CUSTOMER C ON C.CUST_ID = O.CUST_ID

Without left join solution:

SELECT O.*,
(SELECT C.CUST_CODE FROM CUSTOMER C WHERE C.CUST_ID=O.CUST_ID) AS CUST_CODE,
(SELECT C.CUST_NAME FROM CUSTOMER C WHERE C.CUST_ID=O.CUST_ID) AS CUST_NAME,
(SELECT P.PART_CODE FROM PART P WHERE P.PART_ID = O.PART_ID ) AS PART_CODE,
(SELECT P.PART_NAME FROM PART P WHERE P.PART_ID = O.PART_ID ) AS PART_NAME
FROM ORDERS O