5. Mary drives more carefully than Tony. -> Tony drives ......

Tony drives less carefully than Mary.

The phrase "Mary drives more carefully than Tony" indicates that Mary's driving habits are superior in terms of caution and safety. To express this in terms of Tony, we need to highlight his relative driving behavior compared to Mary's. Therefore, saying "Tony drives less carefully than Mary" accurately captures the opposite quality. In comparative statements, the relationship of "more" and "less" helps establish understanding of superiority and inferiority in traits or actions, which is fundamental in comparative grammar.