【单选题】Which of the following statements is NOT true according to the passage?
A.
In the past, people sometimes plugged their ears to fight against the offending noise.
B.
An active noise-cancellation system follows the principle of a wave being flattened by meeting its exact opposite.
C.
The first active noise-cancellation system was made in the 1930s.
D.
Active noise-cancellation systems are now available on the market.
【简答题】Directions: Study the following table carefully and write a composition on Changes in People's Diet. Write an essay of 160-200 words based on the following table. In your essay, you should first descr...
【单选题】在正常使用阶段,钢筋混凝土轴心受拉构件 。
【单选题】关于压杆稳定问题 , 正确的说法是( )
A.
理想中心压杆失稳是指在临界力作用下压杆不能保持直线平衡状态
B.
理想中心压杆失稳是指在临界力作用下压杆不能保持稳定的 , 唯一的直线平衡状态
C.
理想中心压杆在大于或等于临界力的轴向压力作用下将失去稳定性
【判断题】在使用阶段,钢筋混凝土受弯构件是不带裂缝工作的。
【单选题】It can be inferred from the first paragraph that
A.
the 1957 influenza infected 250,000 people in America
B.
Asia was the cradle of the 1957 influenza pandemic in America.
C.
Maurice Hilleman went to Asia to Collect the sample of the influenza
D.
it was quite time-consuming to study the genetic structure of the influenza
【判断题】在使用阶段,钢筋混凝土构件是不带裂缝工作的。
【判断题】在使用阶段,钢筋混凝土受弯构件是不带裂缝工作的。