Which statement is true regarding the above query if one of the values generated by the sub query is NULL?

Evaluate the following SQL statement:
SQL> SELECT cust_id. cust_last_name FROM customers
WHERE cust_credit_limit IN
(select cust_credit_limit
FROM customers
WHERE cust_city=’Singapore’):
Which statement is true regarding the above query if one of the values generated by the sub query
is NULL?

A.
It produces an error.

B.
It executes but returns no rows.

C.
It generates output for NULL as well as the other values produced by the sub query.

D.
It ignores the NULL value and generates output for the other values produced by the sub query.

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tomasiq

I believe answer C is not correct. See following example:
SQL> SELECT * FROM emp;

EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
———- ———- ——— ———- ——— ———- ———- ———-
7839 KING PRESIDENT 17-NOV-81 5000 10
7698 BLAKE MANAGER 7839 01-MAY-81 2850 30
7782 CLARK MANAGER 7839 09-JUN-81 2450 10
7566 JONES MANAGER 7839 02-APR-81 2975 20
7788 SCOTT ANALYST 7566 09-DEC-82 3000 20
7902 FORD ANALYST 7566 03-DEC-81 3000 20
7369 SMITH CLERK 7902 17-DEC-80 800 20
7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30
7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30
7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30
7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30
7876 ADAMS CLERK 7788 12-JAN-83 1100 20
7900 JAMES CLERK 7698 03-DEC-81 950 30
7934 MILLER CLERK 7782 23-JAN-82 1300 10

14 rows selected.

SQL> SELECT * FROM emp WHERE comm IN (SELECT COMM FROM emp WHERE deptno = 30);

EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
———- ———- ——— ———- ——— ———- ———- ———-
7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30
7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30
7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30
7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30

If C would be the right answer, also matches for NULL values would be returned, and all records from emp table would be shown.