Which of the following developments led to an increase in european exploration?  a. the discovery of african gold  b. improved seafaring technologies  c. improved agricultural technologies  d. the discovery of asian silk

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".