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: Believed to be a stowaway on a U.S. military transport near the end of World War II, the brown tree snake (Boiga irregularis) was accidentally introduced to Guam, that previously had no native species of snake. It nearly eliminated the native bird population. The problem was exacerbated because the reptile has no natural predators on the island. The brown tree snake, known locally as the kulebla, is native to northern and eastern coasts of Australia, Papua New Guinea, and the Solomon Islands. While slightly venomous, the snake is relatively harmless to human beings. Although some studies have suggested a high density of these serpents on Guam, residents rarely see the nocturnal creatures. The United States Department of Agriculture has trained detector dogs to keep the snakes out of the island's cargo flow. The United States Geological Survey also has dogs capable of detecting snakes in forested environments around the region's islands.
How many native species of birds did Guam have prior to World War II?