Offshore oil-drilling operations entail an unavoidable risk of an oil spill, but importing oil on tankers presently entails an even greater such risk per barrel of oil. Therefore, if we are to reduce the risk of an oil spill without curtailing our use of oil, we must invest more in offshore operations and import less oil on tankers.

Which of the following, if true, most seriously weakens the argument above?

• ATankers can easily be redesigned so that their use entails less risk of an oil spill.  
• BOil spills caused by tankers have generally been more serious than those caused by offshore operations.  
• CThe impact of offshore operations on the environment can be controlled by careful management.  
• DOffshore operations usually damage the ocean floor, but tankers rarely cause such damage.  
• EImporting oil on tankers is currently less expensive than drilling for it offshore.