Answer :

 Railways began with the urbanization movement in many countries from the start of the industrial revolution, transport and all major cities of the world population, this period has exceeded one million. Developments in the medical field has been also effective herein. The world's remaining undiscovered regions (except for places difficult to reach Antarctica and the Arctic) was discovered and has been instrumental in the world to reveal the precise and detailed map in the 1890s.
This century has caused a rapid decline to live in slavery. British Empire after the Haitian slave revolt, using the rule of the sea and tried to stop the slave trade worldwide. Britain in 1834, the United States, following the civil war in 1865, while Brazil abolished slavery in 1888. Likewise, put an end to slavery in the territory of Russia.

Answer:

A on edge

Explanation: