In this sentence, ”principal” is used as a noun in ”the principal” (referring to a person) and as an adjective in ”the principal reasons” (modifying the noun ”reasons”).
List I | List II |
(A)Fits and starts | (1) At appropriate time |
(B)In less than no time | (II) At intervals |
(C) Once in a blue moon | (III) In a moment |
(D) On the dot | (IV) Rarely |