21. Which of the following are external regulators of the cell cycle? cyclins
b. growth factors
mitotic spindles
d. cancer cells

rising sea temps which are causing coral reefs to bleach and die out

glaciers are melting causing sea levels to rise wgich could flood out land

explanation:

sulfur dioxide

explanation: acid rain is caused by a chemical reaction that begins when compounds like sulfur dioxide and nitrogen oxides are released into the air. these substances can rise very high into the atmosphere, where they mix and react with water, oxygen, and other chemicals to form more acidic pollutants, known as acid rain.

the answer is lactic acid from anaerobic respiration. the acid in lactic acid is what creates sore and burning muscles. if you think about how acid burns that will give you a clue for questions like this.