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Historians tell us that the problem of pollution (1) … (to exist) even in
ancient Troy, but it (2) … (to be) very simple. The citizens of ancient Troy
(3) … (to allow) their refuse to accumulate on the floor until there was
such an amount that their doors would not open. Then they simply (4) …
(to reposition) the doors.
The decrees issued to decrease pollution (5) … (to record) as long ago
as the Middle Ages. In England, smoke-abatement law (6) … (to pass) in
1273, and in 1306 a man (7) … (to execute) for burning coal.
However, the Industrial Revolution changed all prior concepts of pollution.
The introduction of power-driven machinery created a pollution
problem that (8) … (to increase) steadily from the mid-eighteenth century
to the present time. The results of industrial pollution (9) … (to be) water
and air toxification, respiratory diseases, and even death. That (10) …
(to prompt) the Environmental Protection Agencies to establish laws to
regulate levels of air and water pollution.