Stephanie M. answered 04/29/15
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Consonance is the repetition of the same consonant sound in a short period of time. All your options have consonance:
A. One summer day, all day I drove it hard
B. How long it might last, how young it might be
C. Ay, look, and he'll smile thy gloom away
D. At least to know the worst is sweet
However, the best example of a paradox is B. If something lasts a long time, it shouldn't be young, so saying "How long it might last, how young it might be" is a contradiction or paradox.
You could also make an argument for D., since it's somewhat paradoxical. Something that's the worst likely wouldn't be sweet.