By saying One can drive a hundred miles in any direction from Beijing and never cross a healthy river (Line 1, Paragraph 2), the author implies that ______.
A.for quite a large area surrounding Beijing, there is no healthy river in any direction from it.
B.Beijing lacks of water supply as most rivers in nearby provinces are either dried or polluted.
C.to find a healthy river near Beijing, one needs to drive beyond a hundred miles from it.
D.within a hundred miles of Beijing, all the rivers are polluted by the wastes from the capital.