Farmer Dunphy has $$100$$ metres of fencing.  He wants to make a closed rectangular pen.  He uses a long wall for one of the sides.  Each side of the pen is a whole number in metres.  What is the largest area that the pen can be? 
选项为:A:$$125\text{m}^{2}$$  B:$$625\text{m}^{2}$$  C:$$1000\text{m}^{2}$$  D:$$1250\text{m}^{2}$$  E:$$2500\text{m}^{2}$$  请回答其中一个选项.