Which change would create a new ecosystem?(1 point)

A) an introduced species

B) a yearly migration

C) a lake freezing over

D) a dam flooding a valley

D) a dam flooding a valley would create a new ecosystem. The flooding would create a new habitat for aquatic organisms and change the surrounding terrestrial ecosystem. The introduction of a new species or a yearly migration may impact an existing ecosystem, but it would not create a new one. The freezing of a lake is a natural occurrence and would not create a new ecosystem.