题目

单项选择 Nanjing, ___________ old capital of the six dynasties, is becoming _________ beautiful city.    A. a, a             B. the, the           C. the, a                  D. an, the 答案：C已知x为正数，下列求极值的过程正确的是（　　） A、y=x2+2x+4x3≥3•3x2•2x•4x3=6，∴ymin=6B、y=2+x+1x≥3•32•x•1x=332，∴ymin=332C、y=2+x+1x≥2+2x•1x=4∴ymin=4D、y=x(1-x)(1-2x)≤13[3x+(1-x)+(1-2x)3]3=881，∴ymin=881