ALBUQUERQUE, N.M. – Albuquerque ranks as the 20th most dangerous city in the world according to the Crime Index. There are only four U.S. cities that made the top 20. Albuquerque trails Memphis, Baltimore, and Detroit. The Crime Index is based on answers to a survey about general feelings of safety. Residents and visitors take part in that survey. South Africa has the top two most dangerous cities: Caracas, Venezuela is the third most dangerous…