主要用于温度较低、黏度较大的低压小口径的管道的热力管网阀门是( )。
A.闸阀
B.截止阀
C.旋塞阀
D.止回阀
参考答案:C
I didn’t like Aunt Lucy, who _____ without warning and bringing us presents.
A.always turned up
B.has always turned up
C.was always turning up
D.was always turned up
如图所示,一物体自倾角为θ的固定斜面顶端沿水平方向抛出后落在斜面上,物体与斜面接触时速度与水平方向的夹角φ满足
A.tanφ=sinθ
B.tanφ=cosθ
C.tanφ=tanθ
D.tanφ=2tanθ