(A) - (IV): "Walking on air" is an idiom meaning extremely happy/elated, fitting perfectly with getting a promotion.
(B) - (I): "Full of joys of spring" creates a poetic expression about being filled with happiness and vitality.
(C) - (II): "Blissfully unaware" is a common collocation meaning happily ignorant of troubles or problems.
(D) - (III): "Feeling on top of the world" is an idiom expressing extreme happiness and success, appropriate for achieving a Ph.D.
Hence, Option 1: (A) - (IV), (B) - (I), (C) - (II), (D) - (III) -> All four matches create grammatically correct and idiomatically appropriate sentences using common English expressions that convey emotions and states of being -> correct