Read this and answer the question. If the question is unanswerable, say "unanswerable".

In 1579 a number of the northern provinces of the Low Countries signed the Union of Utrecht, in which they promised to support each other in their defence against the Spanish army. This was followed in 1581 by the Act of Abjuration, the declaration of independence of the provinces from Philip II.

In what year was the Union of Utrecht signed?
1579