50. ___ A: They are newer than the formations in most caves. B: They were formed by sulfuric acid. C: They have been artificially preserved. D: They are smaller than those in any other cave.

When fuel enters the crankcase of a diesel engine, it （） A: dilutes the lube oil and reduces its viscosity B: forms sulfuric acid in the lube oil C: causes pitting and failure of the bearings D: causes sludge deposits on valve stem