Final answer:
Horseweed is an example of both an early successional species, also known as a pioneer species, and an r-strategist, due to its ability to quickly colonize disturbed areas and reproduce rapidly.
Step-by-step explanation:
Horseweed is often one of the first plant species to colonize a site after a disturbance such as fire. This plant species is an example of both an early successional species and an r-strategist. Early successional species, also known as pioneer species, are the first to colonize disturbed areas and begin the ecological process of succession. They typically grow fast on poor soil and reproduce rapidly. R-strategists are characterized by high reproductive potential, extensive dispersal abilities, rapid growth rate, and the ability to reproduce under adverse conditions. Therefore, the answer to the student's question is (d) an early successional species and an r-strategist.