The Salto Grande Dam is . an important source of nuclear power
an important source of electricity in Argentina
a means of flood control for Peru
not important to the surrounding countries

in 1897, pershing became a tactical officer at west point, and that's where he was given the nickname "black jack." pershing's first name is "john," for which "jack" is a nickname, and he was a white man who commanded black troops. hence "black jack".