I think the statement that correctly uses commas is, "Tony thought the problem seemed simple. After working on it for an hour, however, he changed his mind." In this statement, it clearly sends the message that after Tony worked on the problem for an hour, he concluded that is was not an easy problem.
national geographic Is a good website to use and wikipedia but I think that will be more confusing cause of the small words they use and half of it I dont understand it
