Q: This task is about creating an unanswerable question based on a given passage. Construct a question that looks relevant to the given context but is unanswerable. Following are a few suggestions about how to create unanswerable questions:
(i) create questions which require satisfying a constraint that is not mentioned in the passage
(ii) create questions which require information beyond what is provided in the passage in order to answer
(iii) replace an existing entity, number, date mentioned in the passage with other entity, number, date and use it in the question
(iv) create a question which is answerable from the passage and then replace one or two words by their antonyms or insert/remove negation words to make it unanswerable.
Passage: In 1579 the northern seven provinces signed the Union of Utrecht, in which they decided to join forces against Spanish rule. The Union of Utrecht is seen as the beginning of the Dutch Republic. In 1580 the new and predominantly Protestant state abolished the bishoprics, including the archbishopric of Utrecht. The stadtholders disapproved of the independent course of the Utrecht bourgeoisie and brought the city under much more direct control of the republic; which shifted the power towards its dominant province Holland. This was the start of a long period of stagnation of trade and development in Utrecht. Utrecht remained an atypical city in the new republic with about 40% Catholic in the mid-17th century, and even more among the elite groups, who included many rural nobility and gentry with town houses there.
A:
Who signed the Union of Utrecht in the 15th century?