I would say that all are necessary but the most important one's (in my opinion) are [2, [5, [7, and [9.
4. make water your drink of choice (D)
carrying nutrients and oxygen to your cells.
flushing bacteria from your bladder.
aiding digestion.
preventing constipation.
normalizing blood pressure.
stabilizing the heartbeat.
cushioning joints.
protecting organs and tissues.
It's also known as the "Thinking person workout".
Always asking the physician is a great idea this is infact true!