WHAT IS THE MAIN TOPIC OF THE PASSAGE

45.

What is the main topic of the passage?

A.

Safety instructions in air travel.

B.

Procedures for evacuating aircraft.

C.

Airline industry accident statistics.

D.

Guidelines for increasing aircraft passengers’ survival.Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correctword(s) for each of the blanks.The search for (46) sources of energy has led in various directions. Many communities areburning garbage and other biological waste products to produce electricity. (47) waste products togases or oil is also an efficient way to dispose of waste.Experimental work is being done to derive syntheticfuels from coal, oil shale and coal tars. But (48) date, the process has proven expensive. Otherexperiments are underway to harness power with giant windmills. Geothermal power, heart form earth, isalsobeing tested.Some experts expect utility companies to revive hydroelectric power derived form streams andrivers. Fifty years ago hydroelectric power provided one third of the electricity used in the United States, buttoday it supplies only four percent. The oceans are (49) potential source of energy. Scientists arestudying ways to convert the energy of ocean currents, tides and waves to electricity. Experiments are alsounderway to make (50) of the temperature differences in ocean water to produce energy.