The students _______ busily when Miss Brown went to get a book she _______ in the office. A. had written, left B. were writing, has left C. had written, had left D. were writing,
42. When Peter was at collage, he paid a __________ visit to the library. A. often B. frequently C. recent D. Fre
9．阅读下面的文字，完成文后各题 为荆棘而感恩 美灵 迎着11月的寒风，推开街边一家花店大门的时候，珊德拉的情绪低落到了极点。一直以来，她都
反应4NH3(g)+5O2(g)4NO(g)+6H2O(g)在10 L密闭容器中进行，半分钟后，水蒸气的物质的量增加了0.45 mol，则此反应的平均速率v(X)(反应物的消耗速率或生成物的生
在正方体中,分别为棱和的中点,若为直线与所成的角,则= .
福建土楼已被列入世界文化遗产名录，在著名的承启楼前有一幅楹联：“一本所生，亲疏无多，何须待分你我；共楼居住，出入相见，最易结重人伦”
There are some ______ on the table. A．orange B．book C．tapes D．apple
对于下列实验现象的描述中，正确的是 A 铁丝在氧气中燃烧，生成四氧化三铁 B. 碳在氧气中燃烧，有红色的火焰 C. 硫在空气中燃烧，
