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: The location on the banks of the river Rhine allowed Utrecht to become an important trade centre in the Northern Netherlands. The growing town Utrecht was granted city rights by Henry V in 1122. When the main flow of the Rhine moved south, the old bed, which still flowed through the heart of the town became evermore canalized; and the wharf system was built as an inner city harbour system. On the wharfs storage facilities (werfkelders) were built, on top of which the main street, including houses was constructed. The wharfs and the cellars are accessible from a platform at water level with stairs descending from the street level to form a unique structure.[nb 2] The relations between the bishop, who controlled many lands outside of the city, and the citizens of Utrecht was not always easy. The bishop, for example dammed the Kromme Rijn at Wijk bij Duurstede to protect his estates from flooding. This threatened shipping for the city and led the city of Utrecht to commission a canal to ensure access to the town for shipping trade: the Vaartse Rijn, connecting Utrecht to the Hollandse IJssel at IJsselstein.
What allowed Utrecht to become a major global trading center?