阅读理解
Many people like animals and raise dogs, cats or some kinds of birds. I love dogs most. My aunt
gave me a dog on my birthday. I called it Wang Wang. It is a little black dog. It is friendly and helpful.
It likes to run and play with me. Sometimes it follows my father around in the field.
One day, my father took off his grey coat and put it on the ground under a big tree. Wang Wang
stood watching him. My father said, " Watch over my coat, Wang Wang. " Wang Wang sat down beside
the coat. My father went to work. After he finished his work, he forgot all about his coat and went home. Later in the evening I can't find my dog. I looked for it everywhere calling, " Wang Wang!Wang Wang!"
But Wang Wang didn't come back. Soon my father wanted something that was in that coat pocket. Then
he remembered Wang Wang. He went back to the big tree. He was surprised but happy. Wang Wang
was sitting on the coat so that nobody could take it away .
1. The writer's favourite animal is_________.
A. cat
B. dog
C. bird
D. pet
2. Wang Wang is ____.
A. helpful and friendly
B. cute and naughty
C. naughty and friendly
D. lovely but unfriendly
3. The dog is ____.
A. grey
B. black and white
C. white
D. black
4. What did the writer's father ask Wang Wang to do under the tree?
A. To watch over the coat.
B. To walk around.
C. To follow him.
D. To play with him.
5. When the writer's father found Wang Wang, Wang Wang was sitting ____.
A. under the small tree
B. on the coat
C. in the field
D. beside the coat
，其中f(s，t)有连续的二阶偏导数，求du及
．