听力原文：Some fuel or oil additives can be a problem for engines and fuel systems. Additives displace protective chemicals in gasoline and engine oil some may corrode fuel pumps or gas tanks, or make flexible fuel hoses and fittings brittle. Instead of enhancing engine life and economy, users might shorten their car's life. Users might shorten their car's life by using some fuel or oil additives which cause engines and fuel systems such problems as displacement of protective chemicals in gasoline and engine oil and corrosion of fuel pumps or gas tanks.