Periodic Table And Periodicity

Electronic configurations of four elements $A, B, C, D$ are given below

(A) $1 s^2 2 s^2 2 p^6 3 s^1$

(B) $1 s^2 2 s^2 2 p^6 3 s^2 3 p^1$

(C) $1 s^2 2 s^2 2 p^6 3 s^2$

(D) $1 s^2 2 s^2 2 p^6 3 s^2 3 p^2$

The correct order of first ionisation enthalpy of these elements is