The difference in water spray pattern between the high-velocity tip and low-velocity applicator used with the all-purpose nozzle is due to（）.

单项选择题The dew point is reached when the（）.

A.temperature of the air equals the temperature of the seawater
B.atmospheric pressure is 14.7 lbs. per square inch
C.relative humidity reaches 50%
D.air becomes saturated with water vapor

单项选择题The design specifications for cranes and crane foundations on ship’s are set and published by the（）.

A.American Society of Mechanical Engineers
B.American Petroleum Institute
C.Society of Petroleum Engineers
D.American Society of Civil Engineers

单项选择题The depth（）a shallow patch，lying about 1.3 miles southeastward of Nanshan Tou lighthouse reduces to about 6.1 meters.

A.above
B.over
C.up
D.upon

单项选择题The datum from which the predicted heights of tides are reckoned in the tide tables is（）.

A.mean low water
B.the same as that used for the charts of the locality
C.the highest possible level
D.given in table three of the tide tables

单项选择题The dangerous semicircle of a typhoon in the Southern Hemisphere is that area（）.

A.measured from due south clockwise 180°
B.measured from due south counterclockwise 180°
C.to the left of the storm's track
D.ahead of the typhoon measured from the storm's track to 90°on each side