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【单选题】
关于精子与受精的描述,下列哪项是错误的?A.
每次射精的精子数少于2000万，即不易使卵子受精
B.
在男子体内，精子由于“去能因子”的影响而处于抑制状态
C.
精子获能的主要部位是子宫腔
D.
月经周期的中期，孕激素使宫颈液变得稀薄，精子容易通过宫颈
E.
精子与卵子一般是在输卵管内结合
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【单选题】Why passengers in a cruise ship sitting in the port of Yokohama were not allowed to leave the ship 14 days ago?
A.
Because all of the passengers in this ship had been infected by new coronavirus.
B.
Because some passenger in this cruise ship were found to have been infected by new coronavirus.
C.
Because they had to be under quarantine.
D.
Because they didn’t want to leave.
【简答题】Why does a ship need maintenance?
【简答题】钳形电流表是一种用于测量 交流电流大小的仪表。
【单选题】Why a gearbox is needed in a ship driven by a medium-speed diesel engine? .
A.
To reduce the main engine speed
B.
To increase the main engine speed
C.
To govern the main engine speed
D.
To fix the propeller shaft
【单选题】According to paragraph 1, why is it difficult to determine when the first clipper ship was built?
A.
The clipper predates written records by almost 75 years.
B.
Sailors kept the details of their vessels tightly guarded secrets.
C.
The clipper has no technical specifications that can be used to identify it.
D.
The term 'clipper' was originally used to describe a variety of ships.
【单选题】Why was Key on board a British ship?
A.
Because he was held after a negotiation with the British.
B.
Because he was arrested during the battle.
C.
Because he could not persuaded the British to set the doctor free.
D.
Because the British began their attack on Baltimore.
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