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

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."
What actually saved the elm?

You have been badly injured in a car accident. It is necessary to give you a blood transfusion because you lost a great deal of blood in the accident. However, special care must be taken in selecting new blood for you. If the blood is too different from your own, the transfusion could kill you. There are four basic types of blood; A, B, AB, and O. A simple test can make sure of a person's blood type. Everybody is born with one of these four types of blood. Blood type, like hair color1 and height, is received from parents. The four groups must be transfused carefully. A and B cannot be mixed. A and B cannot receive AB, but AB may receive A or B. O can give to any other group; therefore, it is often called the universal donor . For the opposite reason, AB is sometimes called the universal recipient . However, because so many reactions can happen in transfusions , patients usually receive only salt of plasma (liquid part of blood) until their blood can be matched as exactly as possible in the blood bank of a hospital. In this way, it is possible to prevent the transfusion from any bad reactions.
People with type A blood can receive type     .

Lamp2a acts as a receptor in the lysosomal membrane for substrate proteins of chaperone-mediated autophagy. Using antibodies specific for the cytosolic tail of lamp2a and others recognizing all lamp2 isoforms, we found that in rat liver lamp2a represents 25% of lamp2s in the lysosome. We show that lamp2a levels in the lysosomal membrane in rat liver and fibroblasts in culture directly correlate with rates of chaperone-mediated autophagy in a variety of physiological and pathological conditions. The concentration of other lamp2s in the lysosomal membrane show no correlation under the same conditions. Furthermore, substrate proteins bind to lamp2a but not to other lamp2s. Four positively-charged amino acids uniquely present in the cytosolic tail of lamp2a are required for the binding of substrate proteins. Lamp2a also distributes to an unique subpopulation of perinuclear lysosomes in cultured fibroblasts in response to serum withdrawal, and lamp2a, more than other lamp2s, tends to multimerize. These characteristics may be important for lamp2a to act as a receptor for chaperone-mediated autophagy.

Which is the receptor for substrates of Chaperone Mediated Autophagy?