第13题: [单项选择]乳磨牙最适宜做窝沟封闭的时间是 A. 1~2岁 B. 3~4岁 C. 5~6岁 D. 7~8岁 E. 9~10岁 参考答案:B
第14题: [单项选择]At the moment the machine ______ at full speed. A. ran B. was running C. had been running D. had run 参考答案:B 答案解析:[解析] 本句意为:此时此刻,机器正在全速运转。 at the moment意为“此刻”,可以推知后面的句子应该选用进行时态。