—I have got a headache. —No wonder. You __________ in front of that computer too long. A. work B. are working C. have been working D. worked 答案:. C。 解析: 由于在电脑前工作太久,所以导致了现在头痛的结果,故空格处应填现在完成时或现在完成进行时,即答案选C。已知实数a、b,且a>b,下列结论中一定成立的是( )A、a2>b2B、ab<1C、2a>2bD、1a<1b