下列图示实验操作中，正确的是（   ）

    Hunting with birds is a very old sport. In some countries the golden eagles are used for hunting wild animals. They are used for hunting foxes and wolves.

    Training an eagle to hunt takes a long time. Hunters catch young eagles by using nets made of hair. After being trained, the eagle is taken to a field. A blindfold (眼罩) over the bird's eyes keeps it quiet until the hunter is ready.

    The eagle sits on the arm of me hunter. The hunter's arm is covered with a long, special glove to protect it from me sharp claws (爪子) of the bird. In the field, as soon as the hunter sees a fox or a wolf, he takes the blindfold off the eagle's eyes. The eagle quickly flies into the air and begins to look for the wild animal.

    The eagle sees the animal and catches it with claws like steel (钢铁). Its mouth and claws are strong enough to hold the animal. Usually, the bird carries the animal back to the hunter. Sometimes fast animals with good eyes can get away.

以a、b、c为边，不能组成直角三角形的是（    ）