The building of the Three Gorges Dam in southern China has not been without controversy. The dam is the largest in the world, and it provides much-needed electricity for the region. However, the dam has also caused significant environmental damage. What key event is introduced in this paragraph? A. the building of the Three Gorges Dam B. the environmental impact of the Three Gorges Dam C. the generation of electricity by the Three Gorges Dam D. the development of controversy about the Three Gorges Dam