Which UPDATE statement is valid?

Examine the structure of the EMPLOYEES table:

Which UPDATE statement is valid?

A.
UPDATE employees
SET first_name = `John’
SET last_name = `Smith’
WHERE employee_id = 180;

B.
UPDATE employees
SET first_name = `John’,
SET last_name = `Smoth’
WHERE employee_id = 180;

C.
UPDATE employee
SET first_name = `John’
AND last_name = `Smith’
WHERE employee_id = 180;

D.
UPDATE employee
SET first_name = `John’,
last_name = `Smith’
WHERE employee_id = 180;