D
Can trees talk? Yes --- but not in words. Scientists have reason to believe that trees do communicate with each other. Not long ago, researchers learned some surprising things. First a willow tree  (柳树) attacked in the woods by caterpillars (毛毛虫) changed the chemistry of its leaves and made them tasteless so that the caterpillars got tired of the leaves and stopped eating them. The even more astonishing, the tree sent out a special vapor--- a signal causing its neighbors to change the chemistry of their own leaves and make themselves taste also terrible.
Communication, of course, doesn’t need to be always in words. We can talk to each other by smiling, raising our shoulders and moving our hands. We know that birds and animals use a whole vocabulary of songs, sounds and movements. Bees dance their signals, flying in certain patterns that tell other bees where to find nectar (花蜜) for honey. So shy shouldn’t trees have ways of sending messages?
71.When attacked, a willow tree will protect itself by _______.
A. changing its leaves’ chemistry         B. changing its leaves’ color
C. talking to caterpillars                      D. sending a special vapor
72. From the passage we know that caterpillars _______.
A. like willow trees                            B. enjoy eating fallen leaves
C. feed on willow tree leaves     D. could communicate with willow trees
73.Caterpillars will stop eating willow tree leaves which _______
A . have a chemical change and become tasteless   B. have a pleasant taste
C. are being attacked                                      D. are communicating
74.According to the passage, how do willow trees communicate with each other?
A. They talk in words.                               B. They send a special vapor.
C. They wave their leaves.                          D. They make special sounds.
75.According to the passage, bees communicate with each other by _______.
A. talking                     B. making unusual sounds
C. singing                     D. flying in certain patterns