As an Example of Rapid Evolutionary Change, One Variety of Agrostis

As an example of rapid evolutionary change, one variety of Agrostis grows much faster on tailings and dumps around abandoned lead mines than does another variety.What is the explanation for this?

A) The high lead content of the soil causes an increase in the mutation rate.
B) Lead stimulates the growth of plants.
C) Selection has favored the development of the lead-resistant variety.
D) Selection has favored the development of the lead-sensitive variety.
E) Lead stimulates the production of poisons that protect the plants against predators.