B-25：blue moon 很少
A: Who plays a more important role in your education. your father or your mother?
A：是你父亲还是你母亲对你教育多些呢？
B: My mother, of course.
B：当然是我母亲了。
A: How about your father?
A：那你父亲呢？
B: He turns out once in a blue moon.
B：我很少见到他。
