材料：

Early on 5 November 1996，the 140，086 tonnes deadweight Malaysian flag bulk carrier Giga 2 was nearing completion of discharge of a cargo of iron ore at No.2 discharge berth，Port KemblA、Due to the vessel&39;s light condition，the unloader could not be positioned over No.1 hold，to remove the 1080 tonnes of cargo remaining in that particular hold．At the suggestion of the shift supervisor，ballast was pumped into No.4 hold，which was permissible under the vessel&39;s operations manual．Pumping of ballast into No.4 hold commenced at 0530．

After the lunch break，two terminal workers descended into No.5 hold，where the unloader was working，to clear iron ore from around the bottom of the forward spiral access ladder．The spiral ladder terminated at the top of the lower stool，six metres above the tank top．They had just completed this task and were about to climb the ladder when the bulkhead to the starboard side of the centre line，between No.5 hold and the ballasted No.4 hold，collapsed．Both workers were immediately engulfed by the deluge and，although one was able to haul himself clear，the other remained submerged．

The shift supervisor was working in his office ashore and，alerted by calls over the radio from the Hatchman，dashed on board and immediately descended the ladder into No.5 hold．Up to his neck in the swirling water and guided by the Hatchman above，he was able to grab hold of the submerged worker．Assisted by another terminal worker，who had followed him into the hold，he was able to haul the unconscious and apparently lifeless worker clear of the water．The shift supervisor then administered cardio-pulmonary resuscitation（CPR），which was successful in restoring breathing in the worker．Very shortly afterwards an ambulance officer arrived on the scene and administered oxygen，before the worker was lifted from the hold and taken to hospital．

问题：

The most probable reason that the unloader could not be positioned over No.1 hold was that ________．

A.the trim was too small

B.the trim was too big

C.the draft was too small

D.the draft was too big

No.4 hold into which ballast water was pumped was a ________．A.special hold which could only be used to adjust the trim and/or draft in cargo operation

B.double bottom tank usually not used as ballast tank

C.ballast tank

D.cargo hold

It is concluded that the depth of ballast water in No.4 Hold ________ before the bulkhead was collapsed．A.less than 1 meter

B.around 1 meter

C.around 2 meters

D.more than 3 meters

Of the following，it is ________ that prevented the submerged worker from hauling himself clear when the bulkhead collapsed．A.his weakness or，possibly，his small figure

B.the big depth of the ballast water

C.the big distance from the lower stool of the spiral ladder to the tank-top in No.5 Hold

D.the strong or swirling current in the ballast water

请帮忙给出每个问题的正确答案和分析，谢谢！