Which one of the following food contaminations would be suspected if the end of a can of tomatoes had begun to swell

If you are just talking about inside the can as it has swollen but not exploded, the inner barrier that allows it to have a shelf life of five years would be affected and the product in the can would no longer be any good to consume. However, if we are speaking that the can exploded and the contents of the can happen to get on other things and or perhaps was not cleaned up properly you would be possibly dealing with what is called, "cross contamination" and is generally heard of in the consumable industry, mostly with meats and dairy, but it is not limited to these types of products.