All of the Following Statements Are True EXCEPT

All of the following statements are true EXCEPT:

A) in four-stroke engines, restrictions in the exhaust can cause backpressure, especially at higher speeds.
B) excessive backpressure increases performance and fuel economy.
C) a small amount of backpressure from the exhaust system is needed to keep the combustion chambers hot enough for more complete combustion.
D) exhaust system flow is not affected in a major way by bends in the pipe as long as the cross-sectional area of the pipe is not diminished.