nown. Its sources lay in the industrialisation of Europe and the techniques for assuring the continuance of this growth were by no means exhausted or compromised in 1900. There had not only been a vast and accelerating flow of commodities available only in (relatively) tiny quantities a century before, but whole new ranges of goods had come into existence. Oil and electricity had joined coal, wood, wind and water as sources of energy. A chemical industry existed which could not have been envisaged in 1800. Growing power and wealth had been used to tap seemingly inexhaustible natural resources, both agricultural and mineral. Railways, electric trams, steamships, motor cars and bicycles gave mil-lions of men a new control over their environment; they accelerated travel from place to place and eased transport for the first time since animals had been harnessed to carts thou-sands of years before. In terms of consumption, or of the services to which they had access, or in the enjoyment of better health, even the mass of the population in develope countries were much better off in 1900 than their predecessors a hundred years before In spite of this cheerful picture, doubts could break in. Even if what might happen in the future were ignored, contemplation of the cost of the new wealth and doubts about the social justice of its distribution were troubling. Most people were still terribly poor, whether or not they lived in rich countries where the illogicalness of this was particularly more striking than in earlier times. Another change in the way men thought about their condition arose over their power to get a livelihood at all. It was not new that men should be without work. What was new that situations should suddenly arise in which the operation of blind forces of boom and slump produced millions of men without work concentrated in great towns. This was "unemployment", the new phenomenon for which a new word had been needed. Nor were the cities themselves yet rid of all the evils which had so struck the first observers of industrial society. By 1900 the majority of western Europeans were town-dwellers and they lived in more than 140 cities of over 100,000 inhabitants in 1914. In some of them, millions of people were cramped, ill-housed, under-pro-vided with schools and fresh air, let alone amusement other than that of the street, and this often in sight of the wealth their society helped to produce. "Slums" was another word invented by the nineteenth century.

Oil and electricity became available as sources of energy ______.

A．after 1900

B．before 1900

C．in about 1800

D．in about 1900