Where does sexual reproduction happen in a plant?
the stem, the roots, the flowers, or the capillaries?

In order to create a new plant the plant has to have both male and female gametes (gametes are sex organs) so the plant transfer them to other to fertilize and the ovules (ovules:the part of the ovary of seed plants that contains the female germ cell and after fertilization becomes the seed) and they grow into seeds.

Abay where the river empties into the sea

Humans can affect weathering and erosion in several ways.  humans cause  increases in acid rain and pollution, which increase the amount of  weathering  agents in the air and water, and then on land.for an easy answer: 1) acid rain2) pollution