原句：

Tom is in the classroom.

否定句：Tom isn't in the classroom.

疑问句：Is Tom in the classroom？

肯定回答：Yes, he is.

否定回答：No, he isn't.

原句：

She is a teacher.

否定句：She isn't a teacher.

疑问句：Is she a teacher？

肯定回答：Yes, she is.

否定回答：No, she isn't.

原句：

They are pandas.

否定句：They aren't pandas.

疑问句：Are they pandas？

肯定回答：Yes, they are.

否定回答：No, they aren't.

原句：

He is a student.

否定句：He isn't a student.

疑问句：Is he a student？

肯定回答：Yes, he is.

否定回答：No, he isn't.

原句：

This is Lucy's pen pal.

否定句：This isn't Lucy's pen pal.

疑问句：Is this Lucy's pen pal？

肯定回答：Yes, it is.

否定回答：No, it isn't.

原句：

Those are his parents.

否定句：Those aren't his parents.

疑问句：Are those his parents？

肯定回答：Yes, they are.

否定回答：No, they aren't.

通过这些例子，可以看到be动词在构成否定句、疑问句以及回答时的变化规律。希望这些例子能帮助你更好地理解和掌握be动词的用法。