if....then....else.......if........then..........e lse.................................if...........t hen............else..................iffffffffffff ffffffffffffffffffffffffffffffffffffff thennnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn nnn.................elseeeeeeeeeeeeeeeeeeeeeeeeeee eeeeeeeeeeeeeeeeeeeeee...........NULLLLLLLLLLLLLLL LLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLL................. ..................nb..........