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which is almost as long as three football fields laid end to end. They
measure some 100 feet (30 metres) wide, or a little wider than a
football field. Their hulls tower more than 60 feet (18 metres) high,
about that of a six-story building.
Anchors keep some drill ships on station while drilling, but
those drilling in deep water require dynamic positioning. Dynamically
positioned drill ships use computer-controlled thrusters and
sophisticated electronic sensors. Thrusters are power units with
propellers that the builder mounts fore and aft on the drill ship's hull
below the waterline. Once the dynamic positioning operator tells a
computer exactly where it should keep the rig positioned, the
computer, using information transmitted by the sensors, automatically
controls the thrusters. The thrusters offset wind, wave, and current
forces that would move the rig away from the desired position.
Whether on land or offshore, and whether large, medium, or
small, all rigs require personnel to operate them. The people who drill
wells usually work for a company whose business involves drilling,
either directly or indirectly. So, let's look next at companies involved
in drilling and the personnel who do the work.

4 Find synonyms in the text for the following words.
a swamp mild
to see a tool
a sobility primary
a team a stream
an appearance

5 Find antonyms in the text for the following words.
Deep sea surface
an offshore rig tiny
light duty round
disassembled

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