单项选择题
The hydraulic oil most likely to thin out when hot and thick when cold would have a viscosity index of（）
A.20 B.40 C.60 D.80
单项选择题 When the steering wheel is turned, oil is directed to the steering gear rams by（）
单项选择题 Rudder position is shown on the bridge by the（）
单项选择题 In an elector-hydraulic steering system, rudder shock is limited by（）
