Based on the provided statements, Species C would most likely be classified as an invasive species in the United States.
Species C, a plant from Japan, grows rapidly (up to a foot per day), smothers low-growing plants, and kills trees. Additionally, it has no natural predators, allowing it to thrive unchecked and disrupt local ecosystems. These characteristics align with the definition of an invasive species, which typically causes harm to the environment, economy, or health of a region.
In contrast, the other species mentioned do not exhibit the same level of detrimental impact on native ecosystems.