During the period 1490—1979 the main progress mentioned in this passage was Siebes’ invention was not a perfect one, because

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问题 During the period 1490—1979 the main progress mentioned in this passage was
Siebes’ invention was not a perfect one, because

选项 A、too great a supply of air could result in a sudden rise to the surface.
B、a sudden dive into deep water could cause the crushing of the body.
C、the air pipe attached to a machine could be above the surface.
D、both A and B.

答案D

解析 由第三段中的"But there were two dangers to...One was...The other was..."可知答案。
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