Which of the following determines how long ago orders that haven’t shipped were received?

a. SELECT order#, shipdate-orderdate delay

FROM orders;

b. SELECT order#, SYSDATE - orderdate

FROM orders

WHERE shipdate IS NULL;

c. SELECT order#, NVL (shipdate, 0)

FROM orders

WHERE orderdate is NULL;

d. SELECT order#, NULL (shipdate)

FROM orders;