Question

Oligonucleotides can be synthesized, one nucleotide at a time, by adding activated monomers to a growing chain. Place the steps of chemical DNA synthesis in the correct order.
The first step is : 3' end of growing oligonucleotide attached to solid support.
Then there is four steps:
A
B
C
D
Steps repeat until all residues are added
E
Oligonucleotide cleaved from solid support
The options are:
1. acid removes DMT protecting group from 5'OH of nucleoside in growing chain
2. activated nucleotide (nucleoside phosphoramidite) adds, forming a 5',3. linkage
3. diisoprophylamio or other group activates the next nucleotide
4. protecting groups on bases and phosphates are removed
5. iodine oxidizes the 5',3' linkage yielding a phosphotriester.

Please tell me which steps go in A through E. I feel like I have tried every combo.