Answer:
"He called his mind his mental blackboard and he would use it to work out the details of an invention and then put it to use in real life."
Step-by-step explanation:
This excerpt from the text can actually show how Nicola Tesla was a genius, because in that way he used to create everything ion his mind and keep track of everything that he was doing, using the mind as a blackboard is something very complicated and to have the ability of creating and experimenting in the mind and then putting that into use in real life is something that only people that are extremely smart can accomplish.