阅读理解。
There are many kinds of ants (蚂蚁) in America. One kind is very strong. People are afraid of it
and animals are afraid of it, too.
These ants are often in big groups. They eat all the animals on their way. They can kill (杀死) and
eat elephants. And they can eat houses. Sometimes they can kill (杀死) people and eat them. When
the ants come near, people leave their homes. But people are sometimes happy after the ants pass by,
because they can see no insects (昆虫) or snakes.
1. Some ants in America can be very ____.
A. ugly
B. strong
C. friendly
D. shy
2. People and animals are afraid of ____.
A. one kind of ants
B. all kinds of ants
C. small ants
D. big ants
3. People get away from the ants because ____.
A. the ants cannot eat and kill elephants
B. the ants cannot eat houses
C. the ants are not often in big groups
D. the ants can kill people
4. Where are the insects or the snake's after the ants pass by?
A. They are under the ground.
B. They go to other places before the ants come.
C. Ants kill and eat them.
D. People kill and eat them.
5. Which is the best title for the story?
A. Ants
B. American Ants
C. Big Ants
D. A Strong Ant
上一点的切线与x轴和y轴围成一个三角形．记切点的横坐标为a．求切线方程和所围成三角形的面积。