阅读理解：阅读下面文章，然后从题后所给的A、B、C、D四个选项中选出最佳答案。
Animals can move from place to place, but plants cannot.
When 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.
Some plants have their own ways to keep animals away.
For 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. This is because the lower leaves are easier for
most animals to reach.
Some 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.
Many plants also have chemical defenses. Some 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.
Many plants depend on both physical and chemical defenses.
A 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.
1．The holly plant has more spines on the lower leaves
because most animals ______.
A．are not tall enough
B．like the lower leaves only
C．are not clever enough
D．can get the lower leaves easily
2．To defend themselves, oak trees use ______.
A．chemical means
B．physical means
C．bitter chemicals
D．sandy materials
3．How does tobacco protect itself against an attack from
a caterpillar?
A．Its leaves fight against the attack by physical means.
B．Its roots send a messenger to discourage the caterpillar.
C．its roots increase the production of nicotine when it
is attacked.
D．Its leaves produce poisonous sand to drive the caterpillar
away.
4．What would be the best title for this passage?
A．Plants and Animals
B．How Plants Defend Themselves
C．Attacks and Defenses
D．How Animals Eat Plant Leaves.
答案与解析：
1．D 解析：从第二段可知“the lower leaves are easier for most animals
to reach”，故选D。
2．B 解析：从第三段可知“oak tree, have thick and hard leaves that
are difficult for animals to eat”，又厚又硬的树叶属于植物保护自己的物理手段。
3．C 解析：从第四段可以看出，tobacco保护自己不受毛虫侵害的办法是产生更多的nicotine。
4．B 解析：因为整篇文章都讲植物是怎样保护他们自己的，故选B。
