Penkov suffered a severe loss when his manufacturing plant, located in a shallow ravine, was flooded during a sustained rainfall. The flooding occurred because City had failed to maintain its storm drain, which was located on City land above Penkov's premises, and because Railroad had failed to maintain its storm drain, which was located on Railroad land below Penkov's premises. The flooding would not have occurred if either one of the two storm drains had been maintained properly. Penkov sued Railroad to recover compensation for his loss. The evidence in the case established that the failures of the two drains were caused by the respective negligence of City and Railroad. There is no special rule City and Railroad. There is no special rule insulating City from liability. In his action against Railroad, Penkov should recover 
nothing, because he should have joined City, without whose negligence he would have suffered no loss.  nothing, unless he introduces evidence that enables the court reasonably to apportion responsibility between City and Railroad.  one-half his loss, in the absence of evidence that enables the court to allocate responsibility fairly between City and Railroad.  all of his loss, because but for Railroad's negligence none of the flooding would have occurred. 