用按时间抽取的基2FFT算法计算N点（N=2L，L为整数）的DFT，共需要作（）次复数乘和（）次复数加。
参考答案：N/2log2N；Nlog2N
胆道蛔虫症的典型临床特点是
A．腹部压疼最显著的部位B．板状腹C．右下腹柔软无压疼D．腹胀肠鸣音消失E．腹式呼吸消失
She likes volleyball, _____ she doesn't like playing it. [ ]
A. but
B. or
C. and
