摘要：【英文原题】 Is Friday the 13th really an unusual event? That is, does the 13th of the month land on a Friday less often than on any other day of the week? 阅读全文

摘要：【英文原题】 Greedy Gift Givers A group of NP (2 ≤ NP ≤ 10) uniquely named friends has decided to exchange gifts of money. Each of these friends might or mi 阅读全文

摘要：【英文原题】 Your Ride Is Here It is a well-known fact that behind every good comet is a UFO. These UFOs often come to collect loyal supporters from here on 阅读全文