题目

若双曲线的焦距是，则正实数（ ）A. B. C. D. 答案：【答案】D【解析】先计算，然后根据，简单计算可得结果.据题意，得，解得.故选：D________ of the road ________ broken down． It needs ________．A. Three-fourths; was; repairedB. Three quarters; has; to repairC. Three-fourth; was; to be repairedD. Three quarters; has; repairing D 【解析】句意：四分之三的路已经坏掉了，它需要被修理。根据分数表达法，当分子超过一时，分母加s，所以排除C；根据break down坏掉和 road之间是主动关系，不用被动语态，排除A/C；need to do一般主语是人，need doing一般主语是物，need to do需要做某事，need doing需要被做；故选D