材料：At 1800，the hydraulic steering system failed once again．The master realized he would

材料：

At 1800，the hydraulic steering system failed once again．The master realized he would require shore assistance to rectify the problem，and diverted towards Portland using the thruster to steer by．The weather at this time was south-south-west force 5．At about three hours later，the thruster drive unit failed due to a leaking fuel injector pipe on the power unit．This was replaced using the spare carried on board．Immediately following the engine restart，an adjacent fuel line failed causing shut down of the unit．With no fuel line spares available，the thruster power unit could not be used．The failure of this unit，and that of the main hydraulic steering system，left the vessel without any steering capability．

At 2155，with the weather deteriorating and no steering，the master contacted the Portland Coastguard and a“Pan pan”message was broadcast．A tow to Portland Harbor was arranged and she arrived alongside at 0240 the following morning．The subsequent investigation found that the main hydraulic steering system failure was due to a seized shuttle valve in the main hydraulic solenoid valve block．The solenoid valve had been recently overhauled．It was thought that the“O”rings fitted to the shuttle valve were of either the wrong type or a defective one．The valve had seized in such a position that hydraulic pressure by-passed the system preventing use of the hand steering．

问题：

The vessel was steered by thruster because ________ failed．

A.the hydraulic steering system

B.the solenoid valve

C.the thruster driving unit

D.the hand steering

The time that the thruster drive unit failed was ________ hrs．A.1800

B.2100

C.2155

D.0240

When the hydraulic steering system failed，________．A.the hand steering system could still be used

B.the auto steering system could still be used

C.both hand and auto steering system were out of use

D.neither and steering system nor auto steering system was out of use

The real reason that caused the hydraulic steering system to fail was that ________．A.no fuel line spare were available

B.the weather was deteriorating

C.the“O”rings fitted to the shuttle valve were of either the wrong type or a defective one

D.the thruster power unit failed

请帮忙给出每个问题的正确答案和分析，谢谢！