The economy of the United states after 1952 was the econnomy of a well-fed,almost fully employed people. Despit occasional alarms, the country escaped any postwar depression and lived in a state of boom. A n economic survey of the year 1955, a typical year of the 1950’s, may be typical as illustrating the rapid economic growth of the decade. The national output was value at 10 percent above that of 1954 (1955 output was estimated at 392 billion dollars). The production of manufacturers was about 40 percent more than it had averaged in the years immediately following World War 2. The country’s business spent about 30billion dollars for new factories and machinery. National income available for spending was almost a third greater than it had been it had been in 1950. Consumers spent about 256 billion dollars; that is about 700 million dollars a day ,or about twenty-five million dollars every hour , all round the clock. Sixty-five million people held jobs and only a little more than two million wanted jobs but could not find them . Only agriculture complained that it was not sharing in the room. To some observers this was an ominous echo of the mid-1920’s . As farmer’s shre of their products declined , marketing costs rose. But there were , among the observers of the national economy, a few who were not as confident as the majority . Those few seemed to fear that the boom could not last and would eventually lead to the oppsite-depression.In Line 3, the word “boom” could best be replaced by（）.
A、nearby explosion
B、thunderous noise
C、general public support
D、rapid economic growth