f. The increasing depletion of oil reserves, along with environmental concerns, have prompted some radical developments
in car design over the past few years.
b. Researchers in the automobile industry are experimenting with different types of engines and fuels as alternatives to the conventional gasoline engines.
c. One new type of engine, which burns diesel oil instead of gasoline, has been avaliable for several years.
e. A further type is the gas turbine engine, which can use fuels made from gasoline, diesel oil, kerosene and other petroleum distillates.
d. Finally, several automobile manufactureres are experimenting with methanol, which is a mixture of gasoline and methyl alcohol, as an automobile fuel.
a. A breakthrough in one of these areas will hopefully provide a means of relieving both the overstretched oil market and the environment.
In these examples the syntactic subject position (to the left of the verb) is manned by the meaningless expletive ("it" or "there"), whose sole purpose is satisfying the extended projection principle , and is nevertheless necessary. In these sentences the topic is never the subject, but is determined pragmatically . In (6) the topic is the whole proposition expressed by the sentence (., the fact that it is raining). In (7) it is "some room". In (8) it is arguably the equality in length of the day and night in some day (rather than the day itself).