Will Give Brainliest if correct! Read the following passage:

At the turn of the 20th century, German math teacher Wilhelm von Osten was trying to prove the intelligence of animals. He tried to teach a cat and a bear how to add, but couldn’t do it. After years of training, he found a horse named Hans who could add, subtract, multiply and read German.
What clue is given that might make you find this suspicious?

He had not found another animal who could do this before.
Horses can’t add.
He was a math teacher, not an animal trainer.
It was only the 20th century, so animals weren’t that skilled yet.