15．（36）FWhen an animal is under attack，it can run away or fight back．Plants certainly cannot run away，and they lack teeth and claws．But plants can defend themselves by using both physical and chemical means．
（37）CFor example，the leaves of the holly plant have sharp spines （刺） that discourage grass-eating animals，Holly leaves on lower branches have more spines than leaves on upper branches．
（38）DSome plants，such as the oak tree，have thick and hard leaves that are difficult for animals to eat．Some grasses may contain a sandy material； eating such grasses wears down the animal's teeth．
（39）ESome plants produce chemicals that taste bitter or cause an unpleasant reaction．Some plants may fight against an attack by increasing the production of these chemicals．When a caterpillar （毛虫） bites a tobacco leaf，the leaf produces a chemical messenger．This messenger sends to the roots the information to produce more nicotine．The higher levels of nicotine discourage the caterpillar．
（40）AA certain plant in China，for instance，has prickly（多刺的） leaves，and each prickle contains poisonous venom （毒液）．A single experience with this kind of plant will teach an animal to stay away from it in the future．
A．Many plants depend on both physical and chemical defenses．
B．Oak trees use physical means to defend themselves．
C．Some plants have their own ways to keep animals away．
D．This is because the lower leaves are easier for most animals to reach．
E．Many plants also have chemical defenses．
F．Animals can move from place to place，but plants cannot．
G．Plants like tobacco，protect themselves against an attack from animals or insects in their own ways．
分析 本文主要讲述的是不能移动的植物是如何保护自己的，有些植物采取了物理学上的方法，有些采取了化学上的方法，让自己免受有关动物的伤害，保护自己．
解答 36-40 FCDEA
36．F上下文语境．根据下句When an animal is under attack，it can run away or fight back．Plants certainly cannot run away可知，当动物受到攻击时，它可以逃跑或者反击，植物肯定就不 能逃跑了，故选F．
37．C 上下文语境．根据下句For example，the leaves of the holly plant have sharp spines （刺） that discourage grass-eating animals，可知，有些植物有自己特有的方法来躲避攻击，比如叶子上有锋利的刺，故选C．
38．D上下文语境．前句提到Holly leaves on lower branches have more spines than leaves on upper branches．
植物矮的叶子比高出的有更多的刺，那是因为矮的叶子更容易被动物吃，故选D．
39．E上下文语境．根据后句Some plants produce chemicals that taste bitter or cause an unpleasant reaction．可知，一些植物会产生化学物质来自我保护，故选E．
40．A上下文语境．根据后句的例子A certain plant in China，for instance，has prickly（多刺的） leaves，and each prickle contains poisonous venom （毒液）．可知，有些植物既用外在的比如刺，也使用内在的比如化学物质来自我保护，故选A．
点评 本文是一篇选句填空阅读，题目主要考查上下文内容联系以及文章内容理解．做题时学生应仔细阅读原文，把握文章主要内容，联系文章上下文内容并结合所给选项含义，从中选出正确答案，一定要做到有理有据，切忌胡乱猜测．
