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某有机物A，它的氧化产物甲和还原产物乙都能和金属钠反应放出H2。甲和乙反应可生成丙，甲和丙均能发生银镜反应。有机物A是              （    ）        A．甲醇 B．甲醛 C．甲酸 D．甲酸甲酯