How did railroads change how mail was delivered?

Railway cars were used to sort mail route. When Railway Mail Service began in 1864, mail was exchanged on nonstop trains by hand. Trains were slowed down so clerks could pass the mail off to one another. Shortly thereafter, this dangerous system was replaced with wooden F-shaped cranes placed trackside.

a big wall across the mexican border so no drugs, terrorist, or illegal immigrants can come through : )    

may i see the answer choices?