Peter Wohlleben works in a forest in Germany. His job is to take care of trees. Before he began his
career, he knew little about trees, but after years of hard work,    21.    . One thing especially changed the
way he sees trees.
     It happened one afternoon when Peter was walking in the forest. A big rock with a very strange shape
caught his eye. He went over and studied it very carefully.    22.    , it was not a rock, but a piece of wood
covered with small green plants. More surprisingly, he saw a little green inside the wood after he cut off a
small part of it. In fact, what Peter found was a tree which was cut down hundreds of years ago. "How
could it be? Without leaves, it couldn’t have lived so long," he thought.    23.    it was because the other
trees around it sent their roots to it underground and kept giving it "food."
      Peter was amazed by what he found    24.    . What does it mean if trees do help each other? Do they
have feelings? Can they talk to each other? Since then, Peter hasn't stopped studying trees. 
forest 森林 especially 特別地
21.
(A) he got to know more about them
(B) he found it boring to work in a forest
(C) he became interested in growing trees
(D) the trees finally grew taller and healthier