I believe the answer is Barbed Wire.
Befor the inventions of barbed wire, the Cattles are let to roam freely across the plains and the owners are required to pay a lot of cowboys to supervise them so they didn't go missing. Witht he invention of barbed wire, they can keep the cattle in a secure place without supervision.
The Prime Meridian is a line of B. longitude and its longitude is defined as 0 degrees in geographical coordinate system. Longitude is a geographic coordinate that is measured in degrees and indicates the east-west position of a point on the surface of the Earth. It is denotes as a greek letter lambda (λ).
Answer:
In the first years of the Revolutionary War, George Washington and his Continental Army faced a threat that proved deadlier than the British: a smallpox epidemic, lasting from 1775-1782. Infrequent outbreaks and wariness of inoculation made his troops very susceptible to the disease. After heavy losses in Boston and Quebec, Washington implemented the first mass immunization policy in American history.
