The correct answer is true.
It is true that smallpox weakened the Aztec and Inca Empires.
Not only smallpox, but many other diseases affected the Native American Indians in South America to the degree of almost wiping them out. Indians from Mesoamerica and South America were clean people that put a lot of emphasis on taking care of their health. When the Spaniards arrived, they brought with them many diseases unknown to the Indians such as smallpox, chickenpox, malaria, influenza, and many others.