Which of the following SQL statements represents the correct usage of the CONCAT function?

Which of the following SQL statements represents the correct usage of the CONCAT function?

A.
SELECT CONCAT(1+2.14,’ results an approximate value of pi’) FROM DUAL;

B.
SELECT CONCAT(1+2.14,” results an approximate value of pi”) FROM DUAL;

C.
SELECT CONCAT(‘1+2.14′,||’ results an approximate value of pi’) FROM DUAL;

D.
SELECT CONCAT(1+2.14,|| results an approximate value of pi) FROM DUAL;