题目

In ancient times the most important examinations were spoken, not written. In the schools of ancient Greece and Rome, testing usually was made up of saying poetry aloud and giving speeches. In the European universities of the Middle Ages, students who were working for advanced degrees had to discuss ques??tions in their field of study with people who had made a spe??cial study of the subject. This custom exists today as part of the process of testing candidates (应试者) for the doctor’s de??gree. Generally, however, modem examinations are written. The written examination, where all studen设函数，则对于任意的实数a和b，a+b＜0是f（a）+f（b）＜0的A.必要不充分条件B.充分不必要条件C.充分且必要条件D.既不充分又不必要条件