Question

they are climbing the tree改为否定句、—般疑问句？

Answer 1

They are climbing the tree.  它们正在爬树

这是一个有be动词的陈述句

（1）变否定句，只需要在be动词“are”后面加“not”即可

整理：They are not climbing the tree.  它们没有在爬树

（2）变一般疑问句，只需要把be动词“are”提前即可

整理：Are they climbing the tree ? 它们正在爬树吗？

Answer 2

否定句：They aren't climbing the tree.
一般疑问句：Are they climbing the tree?