Is "March and April (part of a set illustrating the months of the year)" in the public domain?

Yes, March and April (part of a set illustrating the months of the year) is in the public domain and available for free download under CC0 license.

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March and April (part of a set illustrating the months of the year)

This artwork was created second quarter 18th century.

Antoine Watteau, second quarter 18th century