Identify the topic sentence:
As a result of depleting oil reserves and increasing environmental concerns, radical developments in car design have emerged. To find an alternative to conventional gasoline engines, researchers are experimenting with different types of fuels and engines. An engine which uses diesel oil instead of gasoline has been in existence for many years. There is also the gas turbine engine, which can utilize fuels made from gasoline, diesel oil, kerosene and other petroleum distillates. Finally, many automobile manufacturers are testing methanol as a fuel. Hopefully, a breakthrough in these areas will relieve the overstretched oil market as well as the environment.
