November 9, 1965 was a pleasant day. The evening exodus from the hearts of the great cities had just begun, when, without warning, lights in office towers flickered out and died at 5:16 P.M. Elevators stopped. Traffic lights blinked out. Subway trains ground to a halt. Thousands of feet above, astonished airline pilots saw Manhattan fade, then disappear.

In eight minutes, a near total electrical eclipse had swept over an area slightly smaller than Great Britain crowded with 30 million people. A massive power failure had torn the intricate electrical grid that served parts of eight states and a section of Ontario, Canada.

The Great Blackout, as it came to be called, was the first dramatic warning that the relationship between energy supply and demand had reached a precarious balance in the United States. We know the problem today as the energy crisis, and although we are beginning to appreciate its dimensions, we must for a long time to come continue to feel its effects.

Q. Underline the sentence which supports the conclusion arrived at in question No. 3.