单项选择题

Which of the following does the passage mainly discuss

A．Missiles carried by submerged submarines.
B．Messages sent by submerged submarines.
C．Blue-green lasers used by submerged submarines.
D．The way to send a message to submerged submarines.
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单项选择题
The reference word it ( Sentence 1 , Para. 3 ) refers to ______.
A．the air
B．the ocean
C．the laser beam
D．the submarine
单项选择题
Who would be very much interested in the passage
A．Missile builders.
B．Fishermen.
C．Military scientists.
D．Ship builder.
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