一起重机的钢绳由静止开始匀加速提起质量为m的重物，当重物的速度为v1时，起重机的有用功率达到最大值P，以后，起重机保持该功率不变，继续提升
John as well as the other children who ____ no parents _____ good care of in the village. A.have, is being taken B.have, has taken C.has, is taken D.has, have been taken
如图所示，a、b两端接到电压恒定的电源上，如果c、d两端接一电压表，示数为60V；如接一电流表，示数为3A；如果在c、d间接一电阻R3，则三个电阻消耗
The company had about 20 notebook computer but only one-third____used regularly. Now we have 60 working all day long. A. is B. are C. was D. were
下列各项中字音有错误的一项是：（ ） A．谆谆告诫(zhūn) 谬种流传(niù) 有的放矢(dì shǐ) B．哗众取宠(huá) 钦差大臣(qīn chāi) 滥调(làn) Ｃ．华而不实
下列各组国家中，与我云南省相邻的国家是（ ） A.蒙古、俄罗斯 B.缅甸、老挝 C.尼泊尔、越南 D.阿富汗、巴基斯
The policeman warned the driver _______ so carelessly. A. never to drive B. to never drive C. to not drive
金属材料在人类社会的发展史上一直发挥着重要的作用。人类历史上使用最早的金属 A．铜 B．铁 C．铝
