在神经纤维瘤病Ⅰ型中最常见的中枢神经系统肿瘤为()
A.视网膜母细胞瘤
B.听神经瘤
C.视神经胶质瘤
D.脑膜瘤
E.Wilms瘤
参考答案:C
Neglecting friction, you desire to life a 300 kgs weight with a stress on the hauling part of 100kgs.Which of the following tackles would you use ?().
A.Gun tackle
B.Luff tackle
C.Toe-fold tackle
D.Double-luff tackle
单向阀依靠阀芯前后流体的()来自动启闭,以防介质倒流。
A.温度差
B.流量差
C.液位差
D.压力差