Why are global cities designated as such?

A) They are cities with the longest human habitation, or are designated a UNESCO World Heritage site.
B) They are global economic centers for finance, large corporations, and professional services.
C) They are the urban settlements with the largest populations.
D) They are the cities with the most international travel and cultural exchange.
E) They are urban settlements with the most international shipping, trade, or transportation.

B) They are global economic centers for finance, large corporations, and professional services.