Put the following events of the acid growth hypothesis in order.
1) Cell wall softens and expands.
2) Sugar enters the cell via proton cotransporters.
3) Protons are pumped out of the cell by H⁺- ATPases.
4) Positively charged ions enter the cell.
5) New cellulose microfibrils are produced to extend cell length.
6) Water enters the cell via osmosis, and the cell swells.