OPTION B
$B_{2}CD,BC_{3}D,BCD_{4},B_{5}CD,BC_{6}$
HERE term are BCD(not change), numerical value are 1,2,3,4,5,6
numeric value add like this
IN FIRST TERM 1 WILL ADD WITH FIRST LETTER B
IN SECOND TERM 2 WILL ADD SECOND LETTER C
IN THIRD TERM 3 WILL ADD THIRD LETTER D
IN FOURTH TERM 4 WILL ADD FIRST LETTER B
IN FIFTH TERM 5 WILL ADD SECOND LETTER C
IN SIXTH TERM 6 WILL ADD THIRD LETTER D