The correct option is A K
Here in a row to get second element we leave behind 2 alphabet with respect to first element where as to get the third element we leave behind 5 alphabets with respect to second element in row.For example let us see this in our first row of the puzzle given.We have B at first so let us leave C,D and next alphabet is E which is nothing but second element in that row and we have E now.Let us leave F,G,H,I,J and then we have K which becomes third element in that row.Hence in the last row we have second element as N.If first element is K then we might have left L,M and then wrote second element as N.Hence option A is the correct answer.