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.

Ex Input:
Passage: Machine vision systems often require bright and homogeneous illumination, so features of interest are easier to process. LEDs are often used for this purpose, and this is likely to remain one of their major uses until the price drops low enough to make signaling and illumination uses more widespread. Barcode scanners are the most common example of machine vision, and many low cost products use red LEDs instead of lasers. Optical computer mice are an example of LEDs in machine vision, as it is used to provide an even light source on the surface for the miniature camera within the mouse. LEDs constitute a nearly ideal light source for machine vision systems for several reasons:

Ex Output:
non-LEDs are often used for what type of systems?

Ex Input:
Passage: An alloy is a mixture of metals or a mixture of a metal and another element. Alloys are defined by metallic bonding character. An alloy may be a solid solution of metal elements (a single phase) or a mixture of metallic phases (two or more solutions). Intermetallic compounds are alloys with a defined stoichiometry and crystal structure. Zintl phases are also sometimes considered alloys depending on bond types (see also: Van Arkel-Ketelaar triangle for information on classifying bonding in binary compounds).

Ex Output:
What is always a mixture of metal and other elements?

Ex Input:
Passage: Grande Saline Bay provides temporary anchorage for small vessels while Colombier Bay, to the northwest, has a 4 fathoms patch near mid entrance. In the bight of St. Jean Bay there is a narrow cut through the reef. The north and east sides of the island are fringed, to a short distance from the shore, by a visible coral reef. Reefs are mostly in shallow waters and are clearly visible. The coastal areas abound with beaches and many of these have offshore reefs, some of which are part of a marine reserve.

Ex Output:
How deep is Grande Saline Bay?