instruction:
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.
question:
Passage: Other types of lossy compressors, such as the linear predictive coding (LPC) used with speech, are source-based coders. These coders use a model of the sound's generator (such as the human vocal tract with LPC) to whiten the audio signal (i.e., flatten its spectrum) before quantization. LPC may be thought of as a basic perceptual coding technique: reconstruction of an audio signal using a linear predictor shapes the coder's quantization noise into the spectrum of the target signal, partially masking it.
answer:
What is thought of as a basic signal coding technique?


question:
Passage: The great angiosperm radiation, when a great diversity of angiosperms appears in the fossil record, occurred in the mid-Cretaceous (approximately 100 million years ago). However, a study in 2007 estimated that the division of the five most recent (the genus Ceratophyllum, the family Chloranthaceae, the eudicots, the magnoliids, and the monocots) of the eight main groups occurred around 140 million years ago. By the late Cretaceous, angiosperms appear to have dominated environments formerly occupied by ferns and cycadophytes, but large canopy-forming trees replaced conifers as the dominant trees only close to the end of the Cretaceous 66 million years ago or even later, at the beginning of the Tertiary. The radiation of herbaceous angiosperms occurred much later. Yet, many fossil plants recognizable as belonging to modern families (including beech, oak, maple, and magnolia) had already appeared by the late Cretaceous.
answer:
When does a diversity of magnoliids appear in the fossil record?


question:
Passage: The semi-finals have been played exclusively at the rebuilt Wembley Stadium since 2008, one year after it opened and after it had already hosted a final (in 2007). For the first decade of the competition, the Kennington Oval was used as the semi-final venue. In the period between this first decade and the reopening of Wembley, semi-finals were played at high-capacity neutral venues around England; usually the home grounds of teams not involved in that semi-final, chosen to be roughly equidistant between the two teams for fairness of travel. The top three most used venues in this period were Villa Park in Birmingham (55 times), Hillsborough in Sheffield (34 times) and Old Trafford in Manchester (23 times). The original Wembley Stadium was also used seven times for semi-final, between 1991 and 2000 (the last held there), but not always for fixtures featuring London teams. In 2005, both were held at the Millennium Stadium.
answer:

Where are the semi-finals never played?