为什么轴流式通风机的动叶片要设置成扭曲式的?
参考答案:
轴流式通风机的动叶片设置成扭曲式,可以避免气流从叶片顶部向根部流动,防止影响主气流的运动而降低通风机效率。
—Would you like to go and have some coffee with me?
—I'd like to, but my father _______ for me outside . [ ]
A. waits
B. is waiting
C. will wait
D. waited
支气管哮喘发作时常出现 ()
A.进行性呼吸困难
B.吸气性呼吸困难
C.夜间阵发性呼吸困难
D.呼气性呼吸困难
E.混合性呼吸困难