Teacher: Use a disfluent question or a proper question and find the answer to the question based on the given context or return None if an answer can't be found. A disfluent question is a question that has some interruptions in it while framing. A proper question is the correct form of the question without any disfluency.
Teacher: Now, understand the problem? If you are still confused, see the following example:
proper question: In what year did the U of C become one of 7 founding members of the Association of Chicago Universities?
disfluent question: In what year did Robert Harper or did the U of C become one of 7 founding members of the Association of Chicago Universities?
context: Founded by the American Baptist Education Society with a donation from oil magnate and wealthiest man in history John D. Rockefeller, the University of Chicago was incorporated in 1890; William Rainey Harper became the university's first president in 1891, and the first classes were held in 1892. Both Harper and future president Robert Maynard Hutchins advocated for Chicago's curriculum to be based upon theoretical and perennial issues rather than on applied sciences and commercial utility. With Harper's vision in mind, the University of Chicago also became one of the 14 founding members of the Association of American Universities, an international organization of leading research universities, in 1900.
Solution: None
Reason: The answer to the above question is not found from the context hence it is not answerable so the output is 'None' so it is a positive example.

Now, solve this instance: proper question: How long have humans been impacting the delta for?
disfluent question: What has or how long have humans been impacting the delta for?
context: Since ~3000 yr BP (= years Before Present), human impact is seen in the delta. As a result of increasing land clearance (Bronze Age agriculture), in the upland areas (central Germany), the sediment load of the Rhine has strongly increased and delta growth has sped up. This caused increased flooding and sedimentation, ending peat formation in the delta. The shifting of river channels to new locations, on the floodplain (termed avulsion), was the main process distributing sediment across the subrecent delta. Over the past 6000 years, approximately 80 avulsions have occurred. Direct human impact in the delta started with peat mining, for salt and fuel, from Roman times onward. This was followed by embankment, of the major distributaries and damming of minor distributaries, which took place in the 1113th century AD. Thereafter, canals were dug, bends were short cut and groynes were built, to prevent the river's channels from migrating or silting up.
Student:
None