Answer:
The lake is clear and blue while the sky remains dark and cloudy, ready for a thunderstorm.
Explanation:
Antithetical parallels are the words that seems to contrast each other. The first part of the couplet/ sentence represents a theme that contrasts the theme of the second part of the couplet/ sentence. Antithetical parallelisms are most commonly found in the Bible, like Romans 6:23 "<em>The wages of sin is death, but the gift of God is eternal life, in Christ Jesus our Lord"</em>. Here, the first part of the couplet talks of death whereas the adjoining couplet immediately follows with a promise of eternal life.
Thus, the antithetical parallel for the given sentence will be
The lake is clear and blue <u>while the sky remains dark and cloudy, ready for a thunderstorm.</u>