【单选题】As there is less and less coal and oil, scientists are exploring new ways of making use ofenergy,
A.
6. As there is less and less coal and oil, scientists are exploring new ways of making use of energy, such as sunlight, wind and water for power and fuel. A.primary
【单选题】What made the students in Auckland more excited in the new term?
【单选题】关于主键约束和唯一约束说法错误的是_______。
C.
允许空值的字段不能定义主键约束但可以定义唯一约束
【单选题】UN、IN、ηN、cosφN分别是三相异步电动机额定线电压,线电流、效率和功率因数,则三相异步电动机额定功率PN为( )。
A.
√3 U N I N η N cos φ N
【单选题】Which of the following statements is NOT a way of presenting new vocabulary?
C.
Writing a passage by using new words.
【判断题】视频信号的数字化比声音的数字化要复杂的多,每处理一帧画面都要花费若干秒。
【简答题】有一台三相异步电动机,其铭牌数据如下: P N /kW n N /r · min -1 U N /V η N × 100 cos φ N I st /I N Tst/T N T max /T N 接法 40 1470 380 90 0.9 6.5 1.2 2.0 △ 1、当负载转矩为 250N · m 时,试问在 U=U N 和 U`=0.8U N 两种情况下电动机能否启动? 2、 欲采用Y-△换...
【单选题】有关鳞屑型睑缘炎,错误的是
C.
屈光不正、营养不良,长期使用劣质化妆品可诱发
【单选题】A new library __________.
【判断题】变频器的输出频率是可变的,但输出电压是不变的