A) 5' to 3' direction only B) 5' to 3' direction building one strand and a 3' to 5' direction building the other stand C) 5' to 3' direction building the first half of a strand and a 3' to 5' direction building the second half of a strand D) 3' to 5' direction building the first half of a strand and a 5' to 3' direction building the second half of a strand E) 3' to 5' direction on the "old" 3' to 5' strand