Question

ac vs. dc
in the 1880s, the war of the currents began. thomas edison developed direct current, or
dc, a type of electricity that flows in one direction. by 1887, dc was in use around the
united states. it had some drawbacks, though. converting it to lower or higher voltages
was difficult; that is, the current’s force couldn’t be changed easily. transmitted at the
low voltage needed for use in homes and businesses, it lost power after traveling only a
mile. meanwhile, nikola tesla was working with alternating current, or ac. ac reverses
direction many times per second and can be changed to different voltages. at high
voltage, it can be transmitted efficiently, traveling hundreds of miles with little energy
loss. because of its advantages, ac triumphed by the end of the nineteenth century.
what is the main, or central, idea of the passage?
ac has distinct advantages over dc, so ac won the war of the currents.
ac reverses direction and can be converted to lower or higher voltage.

Explanation:

The passage compares DC (developed by Edison) with its drawbacks (hard to change voltage, power loss over short distance) and AC (developed by Tesla) with its advantages (can change voltage, efficient transmission over long distances). It concludes that due to AC's advantages, it triumphed in the War of the Currents. The first option captures this central idea, while the second only describes a feature of AC, not the overall comparison and outcome.

Answer:

AC has distinct advantages over DC, so AC won the War of the Currents.