生态平衡包括哪些具体内容？

已知曲线C，,直线l。写出曲线c的方程式和直线l的直线方程。

Jack is a teacher of English. He is not young，but he is not old. He has a round face and black hair.He is tall. There are fifty students in his class. They all like him.Now it's in the afternoon. Look，some students are working in the classroom. Jack is there，too.He is helping them to study English. He is a good teacher， and he is a good friend of them all.

()1. What does Jack do?

A. He is a worker.

B. He is a teacher.

C. He is a doctor.

D. He's a nurse.

()2. What colour is his hair?

A. It's black.

B. His heir is white.

C. It is brown.

D. He has yellow hair.

()3. How many students are there in his class?

A. There are fifteen students in his class.

B. There's fifty.

C. He has fifty.

D. There're fifty in it.

()4. Jack is a good teacher，isn't he?

A. Yes ，he isn't.

B. No ，he is.

C. Yes，he's.

D. Yes ，he is.

()5. What are the students doing in the classroom?

A. They are walking there.

B. They are doing their lessons.

C. They are helping their teacher.

在世界戏剧舞台上，中国戏曲艺术最鲜明的特色为 _____和 _____。

《毛诗序》提到诗有 " 六义" ，分别是风、雅、颂、 _____、_____、_____。