单项选择题

A sign of thunderstorm development is a cumulus cloud（）.

A.darkening，growing in size and forming an anvil top
B.that shows extensive vertical development
C.creating cold downdrafts that are felt on the ground
D.All of the above

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A shipmate suffers a heart attack and stops breathing. You must（）.

A.administer oxygen
B.immediately check his pulse and start CPR
C.make the victim comfortable in a bunk
D.immediately give a stimulant，by force if necessary

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A ship having continuous closely spaced transverse strength members is（）.

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