选c sum(left)
下面是微软的帮助：Click the cell (cell: A box formed by the intersection of a row and column in a worksheet or a table, in which you enter information.) in which you want the sum to appear.
On the Table menu, click Formula.
If the cell you selected is at the bottom of a column of numbers, Microsoft Word proposes the formula =SUM(ABOVE). Click OK if this is correct.
If the cell you selected is at the right end of a row of numbers, Word proposes the formula =SUM(LEFT). Click OK if this is correct.
