第20题: [单项选择]{{I}} Questions 17-20 are based on the following passage. You now have 20 seconds to read the questions 17-20.{{/I}}When was dry ice first made A. In the 1920’s. B. In the 1930’s. C. In the 1940’s. D. In the 1950’s. 参考答案:A 答案解析:[解析] 再现分析题。文章中指出Dry ice was first manufactured in 1925．结合年代的表示方法，可知答案是A。
第27题: [单项选择]There are just as many protons in the nucleus as electrons______ around it. A. revolving B. spinning C. rotating D. spiraling 参考答案:A 答案解析:题意是：在原子核中的质子数与______ 它们的电子数相同。 [A] revolving“旋转，绕转”，指某一物体沿一定的轨道围绕着另一物体旋转，符合题意。 [B] spinning“旋转，自转”，
