ComboBox Error in Grid

Hi I have Added the combo box to grid using the following code:

function generateCells(row, cell_data)
{
var this_cells = new Array(CELL_LINE_SIZE);
............
this_cells[2] = "<select style=\"width: 185px;\" NAME=ME_REC_COLUMN_3"+row+" onChange=doChange("+row+","+3+","+"this.value)>"+
" <option selected>Character</option>"+
" <option>Numeric</option>"+
"</select> ";
.............
}

But the Problem is when i press the add row button all previous rows selection gone to default.

If anybody have the solution please reply me.