The correct answer is: Inspection of the purchase invoice.

The purchase invoice, supported by a hire purchase agreement if applicable, provides strongest evidence of ownership. The registration document is not a document of title but is indicative of ownership provided it shows that the vehicle is registered in the name of the company. Inspection of the vehicle confirms its existence and is supportive of ownership, but is not conclusive evidence of ownership. Oral confirmation from the salesman of the company's ownership of the car is again supportive but not in itself conclusive evidence. But taken together, all the other options provide support in confirming the company's title to the vehicle.