PLEASE HURRY 20 POINTS!! What is a possible disadvantage of using a hydroelectric dam as a source of energy?

A Hydroelectric dams can harm the aquatic ecosystems both above and below the dam.

B Hydroelectric dams can harm the atmosphere by producing toxic gas.

C Hydroelectric dams do not produce carbon dioxide emissions.

D Hydroelectric dams do not produce radioactive waste.

If soap hits the floor, is the soap dirty or the floor

Does anyone know a lot about how to: - calculate mass of magnesium metal - calculate the actual yield of magnesium oxide - calculate the theoretical yield of mgo - calculate the percent yield of mgo - determine the percent yield of mgo - determine the average percent yield of mgo i had to do an online lab and its asking these questions but i have no idea where to start or how to be able to find these things. i can post the chart of the data from the lab or if you can tell me exactly how i can find each.

How have the greenhouse gasses increased from the year 2000 to 2018