pls help <3 How can two parents with brown eyes produce an offspring with blue eyes?

a.The recessive trait for blue eyes was present in each of the brown-eyed parents.
b.The genes for brown eyes and blue eyes produce a mixed expression of eye color.
c.The dominant trait for blue eyes blocks expression of the parents’ recessive traits for brown eyes.
d.The dominant trait for brown eyes blocks expression of the recessive trait for blue eyes.