Final answer:
Kentucky bluegrass is more heat hardy than annual bluegrass, making the statement true. The Southeastern United States was one of the world's centers for plant domestication, which is also true.
Step-by-step explanation:
The statement that Kentucky bluegrass has greater heat hardiness than annual bluegrass is true. Kentucky bluegrass is known for its ability to withstand various climates, including some that are warm. However, annual bluegrass prefers cooler temperatures and doesn't have the same level of heat tolerance as Kentucky bluegrass. Therefore, given the choices, the correct answer is a. true.
Regarding the additional statement provided, the fact that "The grass typically flowers earlier and earlier every year as it becomes older with each passing year" is not directly related to heat hardiness but may suggest a plant's adaptation to its growing conditions over time.
As for the independent centers of plant domestication, the present-day Southeastern United States is indeed considered one of the places where plants were domesticated independently. This historical fact would make statement 3 true as well.