The necessary condition refers to a relationship between two sentences. If a false sentence is false, it can be concluded that the B sentence is false, then the A sentence is said to be a necessary condition for the B sentence. According to the above definition, which of the following is a necessary condition for the next sentence? ['The salesperson at the jewelry counter is either a college student or a beautiful girl; the salesperson at the jewelry counter is a beautiful girl.', 'Nanjing has beautiful scenery and pleasant climate; Nanjing has a pleasant climate.', 'The instruments of the Observatory are from the Qing Dynasty and the Song and Yuan Dynasties; the instruments of the Observatory are from the Tang Dynasty.', 'Faye Wong, a university teacher, is a PhD and has experience studying abroad; Faye Wong can be hired as an associate professor.']