Skeletal remains of early humans indicate clearly that our ancestors had fewer dental problems than we have. So, most likely, the diet of early humans was very different from ours. Which one of the following, if true, most strengthens the argument? ['Skeletal remains indicate that some early humans had a significant number of cavities.', 'A healthy diet leads to healthy teeth.', 'Diet is by far the most significant factor contributing to dental health.', 'Early humans had a shorter average life span than we do, and the most serious dental problems now tend to develop late in life.']