After the civil war, which development limited
economic opportunities for african americans in
the south?
(1) creation of military districts
(2) establishment of the freedmen’s bureau
(3) use of the sharecropping system
(4) ratification of the 14th amendment

"(3) use of the sharecropping system" would be the best option, since this system meant that the newly freed African Americans were tied to the land of whites, much like they had been before their freedom. 

This is what i found on google “the first mobile phone call was made 40 years ago today. on april 3, 1973, motorola employee martin cooper stood in midtown manhattan and placed a call to the headquarters of bell labs in new jersey.” i hope this you for what your looking.