What dangerous substance was discovered in China during the Middle Ages while seeking ti elixir of life?

Why did great britain finally send an ambassador to the united states in 1791? a) great britain forgave the colonies for their rebellion. b) the u.s. threatened special trade restrictions on british ships. c) great britain did not want the u.s. to become allies with france. d) the u.s. would seek a closer alliance with spain if great britain did not send an ambassador.