Question

the boy is too small to climb the tree (make it complex)

Answer 1

The boy is so small that he can't climb the tree

Answer 2

The complex form of the sentence “ the boy was too small to climb the tree” will be “ the boy couldn't climb the tree because he was too small”.

Here the boy is the subject and climbing the tree is the action, with the tree being the secondary subject.

By using the subjects and the action appropriately the correct complex form of the sentence can be formed easily, as mentioned