Input: Article: The migration of birds also aids the movement of other species, including those of ectoparasites such as ticks and lice, which in turn may carry micro-organisms including those of concern to human health. Due to the global spread of avian influenza, bird migration has been studied as a possible mechanism of disease transmission, but it has been found not to present a special risk; import of pet and domestic birds is a greater threat. Some viruses that are maintained in birds without lethal effects, such as the West Nile Virus may however be spread by migrating birds. Birds may also have a role in the dispersal of propagules of plants and plankton.

Now answer this question: What virus is maintained in birds without lethal effects?

Output: West Nile Virus

Input: Article: On 9 September the OKL appeared to be backing two strategies. Its round-the-clock bombing of London was an immediate attempt to force the British government to capitulate, but it was also striking at Britain's vital sea communications to achieve a victory through siege. Although the weather was poor, heavy raids took place that afternoon on the London suburbs and the airfield at Farnborough. The day's fighting cost Kesselring and Luftflotte 2 (Air Fleet 2) 24 aircraft, including 13 Bf 109s. Fighter Command lost 17 fighters and six pilots. Over the next few days weather was poor and the next main effort would not be made until 15 September 1940.

Now answer this question: What caused the delay in the effort?

Output: weather was poor

Input: Article: Like Maradona, Ronaldo only stayed a short time before he left for Internazionale. However, new heroes emerged, such as Luis Figo, Patrick Kluivert, Luis Enrique and Rivaldo, and the team won a Copa del Rey and La Liga double in 1998. In 1999, the club celebrated its centenari, winning the Primera Division title, and Rivaldo became the fourth Barcelona player to be awarded European Footballer of the Year. Despite this domestic success, the failure to emulate Real Madrid in the Champions League led to van Gaal and Nunez resigning in 2000.

Now answer this question: When was the centenari of Barcelona celebrated?

Output:
1999