Answer :
The right answer is they help in building bone, and that is done by vitamin D.
Vitamin D is involved in the regulation of calcium metabolism, helping the bones to stay strong and rigid. It modulates immunity: thus, several studies suggest that it could prevent autoimmune diseases. It regulates the blood pressure. It has an anti-cancer and anti-inflammatory power.
In the form of supplements, it prevents or treats rickets, could prevent fractures of osteoporosis, osteomalacia. It lowers blood pressure. It could prevent autoimmune diseases such as multiple sclerosis and type 1 diabetes (childhood diabetes). Evidence that it could prevent cancer and cardiovascular disease is lacking.
Vitamin B9 helps to meet protein needs, synthesize chemical messengers of the brain and nucleic acids for DNA and RNA. But in no case it plays the role of ions and neurotransmitters.
For the other 2 proposals there are no vitamins that perform these functions.