In 1490 or so, the main progress mentioned in this passage was ______. Siebe’s invention was not a perfect one, because ______.

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问题 In 1490 or so, the main progress mentioned in this passage was ______.
Siebe’s 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
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