When a student's day comes, they are to observe the moon in the evening.
(a student's day; comes; ) (they; are; to observe the moon in the evening; T:When a student's day comes) (they; to observe; the moon; T:in the evening)
a student's day they they
comes are to observe
to observe the moon in the evening T:When a student's day comes
the moon T:in the evening