It is C because voluntary trade does not discourage trade (B)
and A and D have nothing to do with it.
The Pullman strike ended with widespread violence and the President at the time (Grover Cleveland) sent out the army to stop the strikes from obstructing the trains from running. The Pullman Strike was a boycott which shut down much of the passenger and freight trains west of Detroit because of reduction wages. Many of these workers were laid off and had their wages lowered, but did not have their rent lowered which was essentially unfair, as they all lived in towns for train workers.
Answer:
known as the central powers
The correct answer is:
The steam engine.
James Watt (1736 – 1819) improved Thomas Newcomen's 1712 Newcomen steam engine. Wat designed his own steam engine in 1776, with a separate condenser that eluded waste of energy, improving the power and efficiency of steam engines. It became key to the Industrial Revolution in Great Britain and all around of the world.