Given a context passage, generate a question from the passage such that its answer is shortest continous span from the passage.

[EX Q]: In the 1950s, a family that owned a farm near Beulah, Michigan kept a bull chained to an elm . The bull paced around the tree, dragging the heavy iron chain, which led to a groove in the bark . The groove deepened over the years. Though for whatever reason, it did not kill the tree. After some years, the family took their bull away. They cut the chain, leaving the loop around the tree and one link hanging down. Then one year, agricultural disaster struck Michigan in the form of Dutch Elm Disease. All of the elms lining the road leading to the farm became infected and died. Everyone thought that the old elm would be the next. The farm owners considered doing the safe thing: pulling it out and cutting it up into firewood before it died. But they simply could not bring themselves to do it. It was as if the old tree had become a family friend. So they decided to let nature take its course. Amazingly, the tree did not die. Nobody could understand why it was the only elm still standing in the county! Plant experts from Michigan State University came out to observe the tree. They observed the scar left by the iron chain, now almost completely covered by bark. The experts decided that it was the chain that saved the elm's life. They reasoned that the tree must have absorbed so much iron from the chain that it became immune to the virus. It's said that what doesn't kill you will make you stronger. Or, as Earnest Hemingway put it, "Life breaks us all, but afterwards, many of us are strongest at the broken places."
[EX A]: What actually saved the elm?

[EX Q]: CADASIL is a cerebrovascular disease caused by mutations in the NOTCH3 gene. Most mutations result in a gain or loss of cysteine residue in one of the 34 epidermal growth factor-like repeats in the extracellular domain of the Notch3 protein, thus sparing the number of cysteine residues. To date, more than 130 different mutations in the NOTCH3 gene have been reported in CADASIL patients, of which 95% are missense point mutations. Many polymorphisms have also been identified in the NOTCH3 coding sequence, some of them leading to amino acid substitutions. The aim of the present study was to analyze the NOTCH3 gene in a large group of patients affected by leukoencephalopathy and to investigate the presence of genetic variants. The molecular analysis revealed several nucleotide alterations. In particular, we identified 20 different mutations, 22 polymorphisms, and 8 genetic variants of unknown pathological significance never reported previously. We hope that this NOTCH3 gene mutational analysis, performed in such a significant number of unrelated and related patients affected by leukoencephalopathy, will help in molecular screening for the NOTCH3 gene, thus contributing to enlargement of the NOTCH3 gene variation database.
[EX A]: Which amino acid residue appears mutated in most of the cases reported with  cadasil syndrome?

[EX Q]: 6141 Durda (1992 YC3) is a Mars-crossing asteroid discovered on December 26, 1992 by Spacewatch at Kitt Peak.
[EX A]:
Who was the original discoverer of 6141 Durda?