Question

I could see a cat _____from the fence its was trying to climb.

Answer 1

I could see a cat falling down from the fence it was trying to climb.

Additional Information:

There is also a typo with the "its" that I corrected for you:

"Its" is a determiner. When you use "its" - it shows that an object belongs to someone.

"It" is a pronoun. When you use "it" - it shows that you are still talking about the noun you used before.

Answer 2

I could see a cat falling from the fence it was trying to climb.