全国铁路网上，三条铁路干线相会合的铁路枢纽是[ ]

A．郑州    

B．徐州    

C．兰州    

D．福州

"Culture shock" occurs as a result of total immersion in new culture. It (51) to "people who have been suddenly transplanted abroad. " Newcomers may be anxious (52) they do not speak the language, know the (53) , or understand people’s behavior in daily life. The visitor finds that "yes" may not always mean "yes", that friendliness does not (54) mean friendship or that statements that appear to be serious are really intended (55) jokes. The foreigner may be unsure as to when to shake hands or embrace, when to (56) conversations, or how to approach a stranger. The (57) . of "culture shock" helps explain feelings of bewilderment and disorientation. Language problems do not account for all the frustrations that people feel. When one is (58) of everything that was once familiar, such as understanding a transportation system, knowing how to register for university classes, (59) knowing how to make friends, difficulties in coping with the new society may (60) .

51（）。

A. occurs

B. appears

C. happens

D. exists