题目

 I ran all the way to school yesterday, otherwise I ______ late for the annual talent show. A. was             B. had been         C. would be        D. would have been 答案： D自从扫描隧道显微镜发明以后，世界上便诞生了一门新兴的学科，这就是“纳米技术”，已知1纳米=0.000000001米，则2.25纳米用科学记数法表示为（    ）米（结果保留两位有效数字）．