Which term best describes the relationship between the words turbulent and serene in the passage?

Read the passage.
Ship captains do what they can to avoid turbulent
weather. Rough, stormy seas can threaten ships,
which is why captains avoid them and favor serene
conditions.
Stormy seas cannot always be avoided, however. In
that case, a ship's ballast-heavy material that is
located in the bottom of a ship and acts as a stabilizer
- is essential.
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